You can purchase pre-cut pieces of cultured marble at most home improvement centers.
Dry-fit the first piece of cultured marble by standing it on the floor against the wall. In this remodel the first piece goes behind the radiator. Make sure it is plumb and level since all of the other pieces will need to line up with each other (Image 1).
To cut around pre-existing floor molding in the bathroom, mark the height of the molding onto the piece of cultured marble (Image 2); then measure how far it extends past the door trim (Image 3). Using a square, transfer these measurements to the cultured marble (Image 4).
When the cuts are done and the piece has been dry-fit to make sure the cuts are correct, flip the piece over and apply a generous bead of adhesive to its back (Image 1), making sure it covers the entire piece.
Maneuver the piece into place and press it onto the wall (Image 2). Keep pressure on it until you are sure that the piece will not release from the wall.
Repeat the same process for each subsequent piece, lining up each one as you go along.