How can i add jumping? I am having trouble doing this, i can make it so that the player jumps but if you hold down space it will just keep adding the force.

Add another logic sensor, a collision sensor, make it so that he can only jump when touching the ground. (spacebar AND collision >> force) Give the ground the property “ground” or something, so that (you can give the same property to other ground objects) and make sure he can’t jump up walls and stuff.