Path of Exile COMPLETE NEWBIE Guide: Standard of Challenge League? SSF or Trading? SC or HC?

Hello guys! Fresh Newbie guide here!
It’s a bit late as it was recorded during ABYSS league, but the core idea behind the video is not related to any specific league or mode.
So what is STANDARD LEAGUE and CHALLENGE LEAGUE? Any reason to play SOLO SELF FOUND or HARDCORE for a new player? Let me explain.