allow the mortar to set for 24 hours.

Mix the grout as per manufacturer's instructions. a good mixture will have a thick, pasty feel to it.

Remove any tile spacers you may have used.

Utilize a trowel to spread the grout along the tile's joints, then diagonally along the joints.

Allow the grout to dry for 3 hours.

use a sponge and water to remove extra grout. The grout should not be level with the tile, instead keep the grout beneath the level of the tile.