The first (and only) tailgate party I have been to was at the women's soccer semi-final in Palo Alto. It was held in the parking lot before the game.
Those always sound like so much fun. Did the tailgate have food?
Yes, everyone brought something to share - alcoholic beverages, food like corn, burgers, salad. It was great.
I would love to go to a tailgate. Where else do people tailgate?
People tailgate at all sorts of places such as sporting events and also non-sporting events like weddings and concerts.
Very cool. Do they tailgate after or just before?
They usually tailgate before the event but occasionally after the game or concert.
I see. What else should I know about tailgates?
Well, they're not supposed to be commercial events, so it is not appreciated if someone is selling items to fans.
So it is mostly just put on by the fans themselves.  I like that.