Place a drop cloth directly under the counter top edge along the floor to catch any dripping grout. Remove any tile spacers between the tiles.
Mix the grout, following the manufacturer's instructions, in a bucket with a mixing stick until smooth. Use the edge of a grout float to apply the silicone grout in a line along the top edge of the counter top. Make the line about 2 inches wide and about 1/4-inch high so that it smooths on easily.
Slide the grout over the top of the counter top edge tiles in a diagonal motion with the grout float edge, covering both the top joint of the edge tiles and the joints along the grout edge of the counter top. Moving at a diagonal will ensure that you don't pop off the tiles by coming at them directly parallel to a tile joint.
Push the grout into the open joints, working down the line of grout and tiles until you've filled in all of the joints. If there's not enough grout in the 2-inch line of grout, widen the line by an inch and continue.
Wipe the grout from the faces of the tiles with a rounded sponge dampened in water. Using a sponge with edges could drag the grout from the joints as well.
Wait an hour for the grout to cure then wipe the tiles with a lint-free cloth to remove any powdered residue.
Brush the grout lines with tile and grout sealer to protect the counter top from moisture stains then wait 72 hours before using the surface.