It depends on what you form you decide to write in. While it is indeed broad, there's a lot of criteria which effectively limits what you can do if you want to ensure high marks.
The 3 main forms to write your context piece in are: expository, persuasive and imaginative. You can do hybrid pieces too that are more than one form; for example, imaginative and persuasive etc.
Ideas: essay, speech, article, editorial, story, diary entries, review, opinionative piece
Generally if you do an
essay (assuming from the topic), it'll probably a formal expository piece (or possibly a persuasive essay). You will have to use TEEL and all that, but some people like using an anecdote to begin and conclude their piece (my teacher hated it when people did that though...) Anyway, pick a form that you do best it - your teacher can tell you that if you submit a few practice pieces of each.
Basically your goal is to explore the ideas brought up by your Context, using your primary text to
illuminate these ideas (if you think of it that way, you'll avoid writing a text response-like answer). The primary text should indeed make up the majority of your "sources", but you are encouraged to pull examples from external sources (other books, documentaries, articles etc) that also relay the big ideas from your Context.
That's probably the basic gist of it

Edit: typo