How am I supposed to write/structure/form my essays? It's hard to know what the examiners are looking for, and it doesn't feel like there's a correct way of doing it the same way there was at GCSE.

Essay writing is a universal skill, and is used across many subjects - once you've learned how to write an essay, it becomes quite obvious that there are a few different skeletons that you can apply to almost any question. In most cases, it's best to present both sides of the argument; don't be afraid to tell the audience which side you think is better - sitting on the fence is worse than being on the wrong side of it, and that's if there's a wrong side to begin with. You can use a chronological order, you can split your essay into the different sides of the argument, you can present the constrasting views within your points - once you know all of the different structures, the only tricky bit is picking the best one for your essay, and fleshing it out with your evidence.

The most important part of your essay is the part that is unique to it, and that is your argument. Writing an essay without one is kind of just like rewriting all the different sources that relate to a topic, the same way a textbook does. Your job is not to be a textbook - it is to read the textbook, and then tell someone who hasn't read it why it's great or terrible and whether or not it's worth their time. Once you have a solid argument (I find that summarising your argument in a single sentence really helps), it starts to become obvious what parts of what sources you need to pick out, because you now know more of what is relevant and what isn't. You have certain guidelines on what kind of evidence you need to include, but the general rule is that as long as it's roughly equally spread between context, literary devices, etc. it should be fine.

Another golden rule with essay writing is clarity - if your writing looks disorganised, the reader can only assume that you don't know what you're talking about, even if you do. Unfair, but in the exam your essay is the only indicator the marker has of your understanding of the subject, so you have to pull out all the stops. Writing in the most concise, efficient terms possible is a really good way to make your writing clear - using poncey language just because you think it makes you sound clever can actually do the opposite! At the end of the day, keep in mind that you're writing for someone to read, so it's always good to remember your audience. Essay writing is a skill that comes with practise, so don't worry about getting it perfect so early on!