[pushkins]

First of all I hope you have actually finished "tiling" before you start the grouting ?

The "stainmaster grout" that HD sells probably isn't the best product out there but it's application is much the same as standard grout.
Get yourself a "grouting trowel" it will look much like a normal trowel except it will have a rubber face. Pour a reasonable amount on to the floor and in a sweeping 45 degree motion across the tiled floor work the grout into the joints, moving any excess grout along with the trowel as you go.
Yes you will end up with an amount of grout left on the tile surface, but if you use enough pressure on the trowel as you work it in this amount is relitively small. It will leave what is called among other things "ghosting" or haze, the trick here is to make sure you have a bucket of fresh CLEAN water and a sponge, as the tile surface starts to get a haze wash it off with a well rinsed out and wrung sponge. The less water left trapped in the sponge the easier the cleaning is to do. Depending on how hard you press on the sponge will also guide you to your final grout depth, the harder you push the more grout it will take out. Make sure you clean the sponge in clean water very regulary.

Depending on your skill level and grouting speed you may need to grout some and then go back and clean the earlier grouted area, then return to grouting.

HINT: DO NOT leave too much grout on textured tiles for too long, it will dry and be much more difficult to remove.

Good Luck