It is called a 'Let'
Do you mean "let"? If so, a let is when a serve touches/nicks the net AND lands in on a player's serve. People call "let" so the server knows their serve hit the net. If a server hits a let, they get to redo their serve.
I am not sure but just call your local tennis place
No, you CANT step over the serving line when you serve in volleyball. The "ref" on the side of the court, on the stand, will call it, and give a point to the opposing team. Usually the line judge should call it....
Let is when the ball goes over the net and lands inside the box but hits the net going over, Let is only on a serve. Net is when the ball hits the net and fails to go get over the net.
Almost all of your joints are used in tennis, but the main ones in a tennis serve are the knee joints, and elbow joints.
Of course! As long as it doesn't hit the net and then go over, it's fine.
You can hit an underhand serve in tennis; however, the overhand serve is more effective because it is more powerful. That is why you don't see the underhand serve used much.
A tennis ball!