Got my first printer, what else do I need? Any tips on setup?

Aloha,

I got an Elegoo Carbon FDM coreXY printer and a roll of PLA from the same brand. I've read that some filament brands are better than others but I figured I'd start easy.

I've taken STLs to the library to print, but I've not done my own before. What's all this slicer stuff? What other software and tools do I need? Thanks!