I picked up a brush and swept the floor. (sweep the floor)
I covered the floor with newspapers before I started painting the ceiling. (cover the floor with carpets/...)
I have just finished mopping the floor. (mop the floor)
She got down on her hands and knees and scrubbed the floor clean. (scrub the floor)
Be careful you don't slip on the wet floor, since I've just spilt some coffee on the floor. (slip on the [wet] floor, spill [coffee / tea] on the floor)
"Fall on the floor" means that something falls indoors, but "fall on the ground" means that something falls outdoors.