Do you have to use a golf tee every time you tee off or can you just play from the ground?

You do need to T-off and it's only when you first start. The first stroke on each hole is done from the Tee (officially, teeing ground), where the player can use a tee (a small wooden or plastic peg) to put his ball on, which makes the tee shot easier. After teeing off, a player hits the ball again from the position at which it came to rest, either from the fairway (where the grass is cut so low that most balls can be easily played) or from the rough (grass cut much longer than fairway grass, or which may be uncut) towards the putting green.