You may have been told that you need to choose a topic, write a thesis, and then find some research to back it up.
But the research process usually isn't a straight line! You can, and should, do some research to refine your topic before committing to it. This video explains:
Now do a search on your topic in Library Search. Take a look at the books and articles that come up. What narrower aspects of your topic are researchers studying? Give a couple examples below. Which of these seems most interesting to you? (If none of them are interesting, stop by the reference desk or meet with a librarian for help finding something that is of interest to you!)
Here's an example, using the topic of the effects of Instagram on teens' mental health. You might respond: "One article that Library Search brings up is on the relationship between Instagram and self-harm, and another article is about the related but slightly different topic of an Instagram cyberbullying intervention. One article that seems most interesting to me is on using Instagram to predict and prevent suicide in teens -- even though it's different from my original topic."