Float is what you do when you're lying on the water. Hopefully you know how to swim, so you can float suspended on the surface of the water, rather than sinking straight to the bottom.
We typically think of the verb float as something you do on the surface of an ocean or pool, but it's possible to float in mid-air too. You just need to be attached to a parachute so you don't come crashing down to the ground. You can also "float on air" in a more figurative sense. For example, if the person you're in love with suddenly gives you flowers, you could float around for hours feeling like your feet aren't touching the ground.