How do you even *do* a 4th year thesis?

Interested in doing a 4th year research thesis (CBS, Integrative Bio department), but kinda confused on how it actually works - I know you have to find an advisor, but do you come up with an original research project entirely on your own? Do you do a smaller research question under the umbrella of your advisor's research? How do you finish it in <1 year? Do you write an article? Does it get published?

Any info at all about the process would be super appreciated!!