Purchase the correct type of glue for gluing materials to galvanized metal. When attaching material to metal without other reinforcement, structural adhesive is the type of glue that will hold.
Load the structural adhesive into a construction-grade glue gun. It will come in cartridges that fit easily on the top of the gun. Refer to the manufacturer's instructions for additional details.
Check to be sure that the galvanized metal surface and the material you're bonding to it are completely dry.
Apply a bead of structural adhesive directly to the edge of the material that you plan to glue to the galvanized metal by applying consistent pressure to the trigger of the glue gun.
Pick up the material by its edges and place it firmly against the galvanized-metal surface. Continue pushing it in place for several seconds to ensure the adhesive bonds the two materials together.