Measure the first span of the countertop edge, along the front. Transfer the measurements to a piece of trim, with two marks on the top of the piece and the measured distance between them.
Lay the trim on your miter saw, positioned as it will be on the front of the counter, so the bottom is sitting on the saw platform and the back is standing against the guard rail.
Slide the piece so one mark is under the saw blade. Swivel the blade to mimic the angle at that end of the countertop. If the end is going to be in an inside corner, swivel the piece 45 degrees inward, so it points toward the middle of the piece. If it's going to an outside corner, swivel it 45 degrees outward. If it's going to end flat against a wall, put the blade at 90 degrees (straight across). Cut it.
Move the trim to put the second mark under the blade. Turn the blade again, depending on the angle you need. Cut it.
Press the trim to the front edge of the counter, cover the wood edge of the counter and the exposed edges of the tiles on the top. Shoot nails with your trim nail gun through every 12 inches along both the top and bottom edges of the trim to secure it.
Repeat for each edge of the counter, pressing the mitered ends together to form the corners.