As long as you have the parts set putting them together is real simple, it's like LEGO blocks. Watching a few YouTube videos on it should help a lot. Configuring BIOS may be a little tricky at first but even that's simplified now with UEFI, one press on default settings should get you going. Installing OS is the last thing and that's as easy and same as installing a game.
There's a first time for everything, you can do it, it's really fun. But more than anything you won't get a better performing PC at the same price buying a pre-build.