Nail backer board, such as a cement-based or green board, to the walls before installing a shower enclosure. Use this type of board instead of drywall, because drywall will be damaged by exposure to moisture. Green board is only water-resistant, but is usually enough if the shower enclosure is fiberglass, porcelain or some other solid material. Cement-based boards are waterproof  encloure and will not allow mold growth. If there is a leak around faucets or a crack in the shower, this is what you want on the walls behind the enclosure.
   Apply caulk along the seams of the shower enclosure. Load a cartridge of waterproof  encloure silicone caulk into your caulk gun. Cut off the tip of the cartridge at an angle, using your utility knife. Press the trigger on the caulk gun to apply a caulk bead to all seams. Apply caulk around fixtures and the outside of the shower where the enclosure meets the floor or wall.
  Run your finger along the bead of caulk to smooth it down and seal it to either side of the seams or openings.
  Hang a curtain rod and liner to keep water from ending up on the floor when the shower is being used.