i know nothing about cpanel's admin side so can somebody please enlighten me?

with plesk you can login as server admin and create a reseller account with unlimited access and limits (traffic, domains). said reseller can then login to plesk with their username and password.

so in cpanel, server admin logs into whm(?) and creates the account the reseller then adds their customers accounts in whm or cpanel?

right or wrong?

Yes the server admin creates reseller accounts through the admin WHM
Resellers can add clients accounts but the admin WHM can also add accounts directly, so both resellers and the server admin can create normal shared accounts

Correct. At least as far as I know. :)