Gideon's first ability causes a creature to attack him if able. If, during its controller's declare attackers step, that creature is tapped, is affected by a spell or ability that says it can't attack, or hasn't been under its controller's control continuously since that player's turn began, then that creature doesn't attack. If there's a cost associated with having that creature attack, its controller isn't forced to pay that cost. If they don't, the creature doesn't have to attack.