onside kick question

[ase]

hi, while i am watching NFL today, i have questions about onside kick.

what is an onside kick? I meant what has to happen to have an onside kick?

normally, you kick the ball in the air, following happen (1)recevnig team catch it in the air (2)the ball hit the ground, receving team get the ball(3)the bal hit the ground, kicking team get/down the ball(receving team still has the possession)

in onside play, as long as the ball go more than 10 yards, even before receving team touch the ball, kicking team can try to get the ball and get the possession of the ball? am i right?

thanks a lot