Nobody knows exactly, can be anything from holding hands to having anal sex. Pretty sure it drives most normal people insane
Bro: yo did you hear, hoe
from our school hooked up jock
Me: No. What did they do?
Bro: They hooked up
Me: Okay but bro, like, what the FUCK DID THEY DO?
Bro: How the hell should i know, i just heard they hooked up! fuck
(and now i searched for what it means on UrbanDictionary.com and still couldn't find an answer)