Before you start researching for your essay, you need to have a broad understanding of the topic you're writing about.
For example, you might be writing about a theorist who's relatively new to you. Maybe you've read a couple of their articles. But in order to write a good essay, you need to understand them in the context of their period in history, and how they relate to other academic writers.
You've probably heard of mind maps, they've been around for centuries. And that's because they're a quick and effective way of writing down information and creating connections. If you don't like mind maps, why not Google alternatives to mind maps and find a solution that does work for you.
For a new theorist, I'd write their name in the middle and branch out with questions like, Who were they? When were they around? Where were they based? What did they say? And why were they saying it? Then I do some Google searches to answer those questions. Credo online and Oxford Reference Online, a great encyclopaedias available through your subject guides on the library website, and they'd help me fill in the gaps and make links with other theorists.
Remember, at this point, you're just trying to get a feel for the topic. So try not to get too bogged down if they're based in Vienna in the 1940s. What else was happening? Who else was writing about similar topics? At that time? Did they agree or disagree? which ideas are most interesting to you?
If you keep asking questions, you'll quickly build up a broad picture of the topic, and then you'll be ready to start more specific research. Your subject guide is full of other resources that will help you find that information.