The success of the first Friday the 13th film had the studio eager to get a sequel out quickly. Some thought was given to making this into an anthology series, but it was eventually decided that this movie should feature Jason. That's right, the kid who drowned which caused his mother to seek revenge. The kid whose only appearance in the first film was as a hallucination. Sure, why not?
From this point on, Jason Voorhees would be the star of the franchise. Even in the one where he was dead, he was still something of a MacGuffin. However, this was a different Jason than the one we're all used to now. This early version of Jason made the most sense, though. Knowing the story of Jason as was told in the first film, and accepting for the moment that he didn't really drown, this portrayal is what I would expect the character to be. The changes to the character were gradual, but noticeable. Even maniacal killers develop and grow as people over time, I guess.
I was still pretty young when this was released, so I don't recall if it had been revealed that Jason was to be featured or even if there was any speculation to that effect. I do recall that I was aware of this fact when I first watched it on home video, and I was looking forward to seeing Jason in action. Knowing the character that he would become, the series was on part six at the time, I was a bit confused by this early appearance of Jason. For all I knew this could be misdirection, maybe this wasn't Jason. By the end it was clear, however, though some confusion remained. But let's start at the beginning...
In the first film, we know that Jason is believed dead, drowned as a boy in Crystal Lake. We know via flashbacks that he has some deformities, and it is implied he is mentally underdeveloped. We see him jump out of the water at the end, with his body intact but covered in algae, however, whether or not that really happened is not made clear. Some behind-the-scenes knowledge tells us that this scene was included simply as one last scare and is not to be taken seriously, therefore we can assume it was just a dream or hallucination, but we'll leave it as a possibility that it actually happened. We do know that Jason is alive, as we see later on in no uncertain terms, so this leaves the following possibilities: Jason somehow survived his apparent drowning, or Jason somehow came back to life when his mother was killed. Keeping those possibilities in mind, let's look at the time-frame.
Jason was around 11 when he supposedly drowned. If he was in fact dead at the bottom of the lake, he would have physically remained 11 years old, and that is how he appears to Alice when she sees him jump out of the water. If it was Jason who killed her two months later, he would have had to become fully grown during those two months. If it wasn't Jason, and we don't see him until we jump ahead five years, he would physically only be 16 by that point, and that doesn't fit with the character we see on the screen.
If Jason didn't die from his apparent drowning, somehow making it to shore unseen, recovering, perhaps getting lost in the woods, unable to find anyone, he would be completely feral by the time the camp opened again 20 years later. He would have been in his mid-thirties when Alice is killed, and in his late-thirties when the counselor training camp opens five years later. This better matches the character we see on screen. This is the more feasible possibility. No supernatural explanation is necessary, at least not at this point in the series.
So we have a reasonable explanation of how Jason is even around to be in this movie, and also have established his likely mental state after being alone in the woods for over 20 years. Now, let's take a look at the opening scene in part two. Someone, presumably Jason, finds Alice in order to avenge his mother's death. I say presumably, because it is never made clear whether or not this is actually Jason. When you think about it in relation to Jason's character as portrayed in this film, there are some problems. Alice is at home, presumably in a residential area somewhere in the vicinity of Crystal Lake. Jason is in a shack out in the woods, a feral boy in a man's body, eating small animals to survive, his only companion is his mom's severed head. How, exactly, does Jason find this woman's name, find out where she lives, and get there to kill her without being noticed? One possible explanation is that he had help.
Using some behind-the-scenes knowledge once again, we know there were plans in the sixth film to introduce Jason's father, Elias Voorhees. It would have been revealed that he was the one who paid for Jason's burial, and the implication would be he was also responsible for Jason's mother's grave as seen in the fourth film. Elias has only one canonical mention in any of the films, but that is enough to establish his existence, and thus he can be used as a sort of deus ex machina type of plot device for any theories formed to explain away plot holes. After all, Elias making contact with his long lost son while out at Crystal Lake to assist the police with the investigation into Mrs. Voorhees and helping Jason take his revenge, contrived as that may be, is easier to accept than Jason figuring all that out on his own.
Feral Jason
Friday the 13th part 2 introduces the real Jason Voorhees. Not a flashback, not a dream, the real deal. In this case, he's a feral human who has had little to no human contact since he was a child. He is still very upset by the loss of his mother and views everyone as a threat as he protects all that he has left of her. He's dressed in some old clothes he found somewhere, probably from a clothes line or a camp site, and is obviously self aware enough to know his face is different than other peoples' and thus wears a sack over his head.
Jason's portrayal in this film is quite different from all of the following installments. Here, Jason is not the type of killer who is always behind you no matter how fast you run; he's more of a wild animal, sneaking around, waiting for the right moment to strike. He'll let you catch a glimpse of him so that you'll chase him to his lair where he can attack. Each successive installment in the series moves further away from this portrayal, which is too bad because the bolder he gets, the less interesting he becomes.
The writer of the first film, Victor Miller, stated that Jason "was a victim, not a villain." Of course, this was a criticism of using Jason in the sequels when he was already dead in the first movie, but it still holds true to a certain extent when he's alive. In the scene where Ginny is trying to make Jason think she is his mother, you see him look up at Ginny through that hole in the sack on his head. The look in that one visible eye is one of pacification. His mother is telling him everything will be alright, as if to assure him no one will hurt either of them anymore. That little boy is still in there.
A case could be made that this deception is what tips the balance from a scared man-child over to the raging maniac that you see in later installments. Perhaps, in his simple mind, he felt that his mother had betrayed him at that point. Regardless of what might have gone through his head, this is the last time we get to see any solid remnant of the child-Jason, apart from a fleeting glimpse here and there.
Domesticated Conclusions
The theories that have been developed to explain the various inconsistencies in these films can fill hundreds of pages of discussion. There really is no good explanation for how Jason survived drowning, or any of the plot holes and continuity issues. The real answer is that these movies were put together in a short amount of time, before the home video market was really a thing, and the people who made these films didn't think people would care or even notice.
In the days before the home video market, these movies would be watched once and most of the details would be forgotten over the next year or two that it took for the release of the next installment. Now fans can watch them all over and over again and pick out every minute detail that's not perfect. Yes, people go overboard with this, but to be fair, disregarding the continuity established in earlier films is lazy storytelling.
A good way to view this franchise is in the context of its setting. This all began at a summer camp, where stories and legends are told around campfires. Every good legend is based in fact. If you look at the original Friday The 13th as the fact, the event that happened in the past, and then look at Friday The 13th part 2 and all future sequels as the legends that were told based upon the actual event, the continuity issues don't matter as much. The legend of Jason Voorhees grew with each new story told, and one story might contradict another. That's just what happens with legends. Of course, I'll still complain about these inconsistencies, because that's what I do.