The Float has the ability to make things float, as the name implies. The main body of Float is a purple and magenta-striped ballon with wings, similar to the picture depicted on the card. The Float is mischievous card, but also gentle, so it was no trouble to capture. It is under The Windy.
The Float is released in Episode 15, where it starts levitating everything in a child's room, even the child herself. Cerberus finds the card and notifies Sakura of it's whereabouts via fax. Sakura arrives just in time to capture Float before it took the girl up past the atmosphere, but the girl starts the fall and Sakura cushions her fall with The Wood. Float was then used in Episode 17 to cross a chasm in the cave to where The Erase was.
The Float is transformed into a Sakura Card in Episode 57 when Sakura fell into the darkness of the hole Eriol formed on the elevator wall. She transformed Float mid-fall and used it to return to Syaoran, who was also in the elevator when Eriol stopped it with magic.