Cut the end of the nozzle on a tube of caulk at a 45 degree angle using a utility knife. Poke the foil at the bottom of the nozzle using the metal rod attached to the caulk gun. Place the tube of caulk in the caulk gun cradle and push the plunger into its back. Turn the plunger handle 180 degrees and press the release button.
Fill the space around the edge of the tile backsplash by holding the angled end of the caulk tube flat against one end. Squeeze the trigger evenly as you move the caulk gun smoothly along the length of the space. Ensure that an even bead of caulk fills the entire space.
Drag the side of your thumb along the bead of caulk to press the caulk into the crevice and form a bond between the backsplash and the wall or counter that it butts. Wipe the excess caulk off your thumb frequently on a damp rag.
Continue filling the spaces you see around the edge of the backsplash by repeating the procedure. Allow the caulk to dry for 24 hours before exposing it to moisture.