The official backgammon tournament rules allow to put all 15 checkers on a point. If you want to play with a maximum of 5 checkers, go to the menu Settings and activate the Egyptian Rule. Notice, the Egyptian Rule is not in the standard rules of backgammon. The position evaluator in GNU Backgammon doesn't have a clue about how to evaluate positions according to the Egyptian rule either. It strongly recommended that this rule is not used if you're trying to learn backgammon.