Exactly. Friday at school you would talk to friends, "Hey what's everybody doing tonight? Any parties?" Or if there was a football game or basketball game, "What's going on after the game?" There were places where we would normally hang out - like the mall or McD's or a pizza place - where you would run into people that you know and just invite people over or find out where other people were going.
Once a month or so, someone's parents would be out of town, and lots of people would show up. But most often, it was just a few friends in somebody's basement or back porch where their parents didn't mind people being there - and conveniently ignored any drinking.