depending on the tile you installed you may need to seal the tile its self. if the finish is not coated ( like taracotta, slate, or tumbled marble) then you must seal it to keep the dirt out. (typicaly done before installing them)
the difference in sealers are vast. You have the topical sealers, ( silicone) then the penetrating sealers. I would suggest two coats of the penetrating sealer. apply 2 hrs apart and they have 5, 10 and 15 years of wear.