I am not 100% sure (I don't really use the discover feed tbh) but I think it's based on what you interact with the most mixed in with stuff based on your likes, reposts, etc. But that is also very customisable since it allows you to select what you want to see/not see.

Overall, it is still more beneficial to share stuff rather than just liking it since just liking it won't show it to people who follow you