as someone who just searched for that yesterday, i will give you what i have learned because i couldn't find straight answer nor a video explaining the connector. but this is what i get from skimming some long articles.
ATX Connector or Main connector (20+4Pin): for the motherboard
EPS Connector (4+4-Pin): for the CPU connected to the motherboard
PCI-E Connector: for the GPU
SATA Connector: for the HDD , SSD and i think for the optical drives also
Peripheral Connector: i forgot for what because i didn't need them
Floppy Connector: for floppy
here is an
article i found explaining all connectors including some old ones that aren't in your PSU so read about the ones mentioned above