no clue what im doing

-windows 10 home n 64 bit -gigabyte z390 sli gaming motherboard -i7 8700k intel processor @ 3.7 ghz 6 cores -evga geforce rtx 2060 gpu -16 gb ram -reused power supply The PC is able to run some games while completely crashing on others, even though all system requirements are met. my knowledge...