Grout and Sealer

Grout - Grout is a type of cement that is used to fill the space and provide support in tile joints. Portland cement based, and epoxy based are the two types of grout commonly used. Pigment is added to the cement providing an assortment of color options.
Sanded Grout - Both types of grout may have sand added to provide additional strength to the tile joint. Sanded grout is recommended for tile joints 1/8th of an inch and larger.
Unsanded Grout - Unsanded grout is recommended for tile joints less than 1/8th of an inch.

The sealing of ceramic and stone tile must be evaluated on a case to case basis. Be sure of why you are sealing your tile, and closely follow the Manufacturers instructions.
The first step in stone tile maintenance is the sealing of the stone. Generally, all stone must be sealed.
Glazed tiles should never be sealed. The glaze is far more permanent and resistant to wear than any sealer.
Many people seal their tile that is installed indoors to protect against everyday dirt, stains and wear.