I Bought GA tickets for a concert is it going to be by seats or first come first served ?

No seats on bottom standing only. If you want a seat its on balcony level

Depends. Some shows have seats for GA and some don't. I saw Buddy Guy there this past sunday and there were chairs on the GA floor and they were all first come first served.

Standing on bottom sitting on top

Its mostly on a first come first serve basis. There were two sections on the floor level that are sectioned off. Either way the floor level (GA) with no listed number usually means you stand wherever you like. You will lose your spot if you decide to hit the bar and whatnot. This was for a Jhene Aiko type of concert.

first come first served

(general) says it all coda