Priority works like this: Whoever’s turn it is, they are the ‘active player’. The active player has priority but passes it temporarily each time he or she does something. Then his or her opponent receives priority (the ability to play spells), so they can play an instant in response to the spell played by the active player. Once they decide what to do, (play an instant or do nothing) priority goes back to the active player and they can play an additional spell to be placed on top of the stack to be resolved before their first one. Usually they do not and the spell resolves. Priority does not give you the ability to play anything you want. Sorceries and Creature spells can only be played on your turn and when nothing is on the stack. Instances and Creatures’ activated abilities go on the stack and can be played at any time.