It's pre-installed, just search for it via the search bar which is located in the upper right hand corner of your screen.
Drag it to the task bar then left click it you should see new screen recording and from there on record what you want or look up a tutorial on youtube but QuickTime has no editing service so you may only record not edit.
I use (or try to) obs, this drops me like 10 fps. Idk how good your computer is, so it might not affect you.
