Golfers know they can't tee up their ball on a hole ahead of the tee markers from the tees they're playing. That's against the rules and comes with a severe penalty of two strokes and then needing to play a ball from what' s officially dubbed the teeing ground.
However, not every golfer knows how far behind the tee markers they can tee up the ball and not suffer a penalty stroke.
Basically, a golfer can draw an imaginary rectangle to determine where they can tee up their ball on any hole. First, two corners of the rectangle are the tee markers. You can't tee the ball in front of them, and you can't tee the ball up outside of them.
Second, the rest of the rectangle is created by taking two full clublengths (up to the longest club in the bag, which is almost always driver), from behind each of the tee markers. The rectangle is finished by completing the imaginary, tee marker-wide line running from the two points created by going two full clublengths behind the tee markers.
Now, while the golf ball can't be teed up outside of this rectangle, the Rules of Golf don't prohibit a golfer from standing outside this rectangle. Only the ball has to be in it.
All of this is covered under Rule 11 of the current Rules of Golf. The space is created so a golfer can feel comfortable hitting a tee shot on a space where there could be plenty of damaged turf, particularly on a par 3. The real estate created by the imaginary rectangle on the teeing ground behind the tee markers gives plenty of space to confidently tee up the ball and also have the space to hit the desired tee shot shape.