So I thought, I could explain it for those who does'nt know :)
Basically Generation 1 is the first pony sort that came out, and with sort I mean how they look and so on.
And yeah that's it :D There is a Generation1, Generation2, Generation3, Generation3.5 and a Generation4!
And here are pictures of them in order ofc!
My G1 Lemondrop
My G2 IvyMy G3 Frilly Frocks
My G3.5 Sweetie Belle
And My G4's FlutterShy, Pinkie Pie, AppleJack, Rarity and her little sister Sweetie Belle.