If your tile is porous or unsealed, the tile manufacturer may recommend applying a sealer to the tile before you grout. Grout can stain or stick tightly to porous or unsealed tile.
Mix the grout to proper consistency (premixed grout is a lot easier to work with than bulk grout). Remove the tile spacers and start adding grout in the furthest corner from the door to avoid walking on finished grout that is still wet. Working in sections, apply grout liberally with a rubber float. As you work, clean excess grout off the tile faces with a coarse cloth or damp sponge, but be careful not to wet the grout, which will weaken it. Wipe diagonally across the joints to avoid pulling the still-fresh grout out of the grooves.
After the grout has dried thoroughly, use a release agent to clean grout haze from the face of the tiles, then apply a grout sealer according to the product directions.