Measure the first wall at the floor, from one corner outward to the end, just above the tile floor. Mark the measurement on a piece of baseboard molding, with two marks on the top of the molding with the measured distance between them.
Set the molding on the miter saw, standing the molding in the position it will be against the wall. Set the molding so one of the two marks is under the blade.
Swivel the blade 45 degrees inward, pointing it toward the middle of the molding. Make the cut.
Move the molding so the other pencil mark is under the blade. Turn the blade so it’s facing 45 degrees inward, which is the opposite direction as it was pointed before.
Cut the molding.
Repeat the measuring and cutting of the baseboard molding for each piece.
Set each piece of molding against the wall, sitting on the ceramic floor, with the mitered ends tightly butted in the corners. Shoot trim nails through the face of the molding and into the walls (not the floor) with two nails every 10 or 12 inches along the length of each piece; shoot one nail along the top and the other along the bottom.
Caulk along the base of the molding where it sits on the ceramic tile. Flatten each bead of caulk with your thumb after you apply it so it completely fills the gaps created by the grout lines of the tiles and ties the tiles to the baseboard.