The Nova Project.

[Kaden]

Thinking about it, I don't know if I would get into League if I was just starting now. God damn is there a lot of stuff to learn.

Yeah, I think the same thing often. Seems daunting.

The most common situational elements you'll run into are CC, tankiness, and damage type. As Vad pointed out, Galio is good against lots of magic damage. Tryg already explained Kat and CC. Champions like Kog, Vayne, Malz, and Nasus are good against tankier teams because of their %-based damage.

There are more specific cases (no hard-CC, but everyone can permaslow; everyone has a blink; everyone has a heal; etc.) but those are really the most common things you'll want to be aware of when thinking about "counter" picking a comp.