I have a 08' scion xb with a built in gps system/cd/dvd player. how do you play dvds? ?

You have to have the car in park, and the parking brake on to play DVDs on the in dash dvd player. This is a requirement by law so you are not distracted by video while driving. Also, that book in the glove box also known as the owner's manual will give you the proper instructions.