Oh geez...

Inside the carburetor is a float that operates a needle and seat valve. The needle and seat valve shuts off fuel flow into the carburetor so that the fuel pump can't pressurize the carburetor, which would start force-feeding the engine fuel.

In the float bowl, the float is the "switch" that tells the needle and seat when to open and close. When the fuel level in the float bowl drops, like in a high demand situation [WOT], the float drops as well and the needle and seat open again, and fuel is allowed to try and re-fill the float. Likewise, if the engine is not consuming a lot of fuel, such as an idle condition, then the float bowl level will be high. When the float reaches it's set point, it closes the needle and seat, and doesn't allow any more fuel to enter the float bowl until the level goes back down.