Never built a pc

Thinking of building a pc. I don’t need aesthetics at all just performance and I need it to be able to run fl studio well which usually means decent ram and a good cpu. I play games a good amount especially during summer and I don’t ever mind running low settings but I want to be able to perform well and upgrade from what I have. My friend gifted me a really bad pc (not complaining) but I can’t run fl with the bad cpu. Was trying to keep it around 700$. Any help is appreciated!