Clear penetrating grout sealers are a transparent liquid specially formulated to provide stain protection to absorbent grout. There are a few different types of clear sealer, some specifically designed for stone tiles and those designed for grout only.
Clear sealers are a mix of polymers or flourochemicals in a solvent or water based solution depending on it’s intended use.
A professional can evaluate your surface and determine the best choice of sealer for your situation.