Still mystery to me - different brands

Coastal South Carolina
i go in waldo mart supetech at 84 cents (throw them out cause of quality concerns and walmart specifies "cheap" But consider Mobil "clean" oil at $110 havoline at 1.26 some of the castrols, quakers at 1.76 and maybe other for a touch more 2.10 not counting premisum oils I have read a lot of these forum topics and have a somewhat chemical background (hey maybe thats the problem) I can not really tell what the differences are. people talk about group one, 2 etc and all their favorites etc. Is there a summary anywhere? Or is it like consumer reports said, all api graded oils are the same?????