I am getting ready to GM my first game and have a quick question about advantage. I haven't found this answer in the Core Rulebook or I have missed it. Do any generated advantage generated on a roll, especially a combat roll, have to be spent on that turn or can players stack advantages to spend whenever they want?

Thanks for clearing up my confusion.

They must be cleared on that roll to my understanding. You can use it to add a boost to their next roll to help generate more advantage the next time, but normally the advantage on the roll is spent on the same roll.

It wouldn't make any sense if they saved 3A from shooting a blaster, then turned around and added them to 2A they got slicing a computer. They aren't "luck points" to be used for whatever purpose, they are narrative tools to be applied related to the skill check in question.