Can someone explain valence electrons and principal energy levels to me? They are kinda confusing.

Valence electrons are the electrons which are located in the last shell of the element. like oxygen has 6 valences electrons located in its last shell. Principal energy levels are also know as sub shells. in direct or easy words shells or orbitals. starting from 1s 2s 2p 3s 3p 3d 4s 4p 4d and etc.