Summarize the following:
Existing grout should be cleaned and dried before resealing. Make sure grout lines aren't cracked, chipped, or otherwise compromised before treating with a sealant. If they are, touch up grout and wait the requisite 48 to 72 hours before sealing. It is important to tape off these other surfaces to prevent unintentional staining. Coat the grout lines, making sure you cover the grout joints completely. If the sealer gets on the tile, take a damp cloth and wipe the sealer off. Apply the second coat and wait another 5 to 15 minutes. Use a clean, dry color appropriate towel. Use water and a white nylon pad or any clean cloth to scrub residue from dried grout sealant on tiles. Most sealers are dry to walk on in 2-5 hours. Keep anything that can stain the grout away for 72 hours. A full sealer cure is usually achieved in 24 to 48 hours. Test the effectiveness of the grout sealant by flicking a few drops of water onto the grout line. An effective grout sealant will cause the water to puddle on top of the grout. If the grout absorbs the water, reapply sealer. Try this at various locations on the grout lines.

Summary:
Allow new grout to cure for 48 to 72 hours before sealing. Tape off baseboards and other nearby surfaces. Apply sealer using a foam paint brush, paint pad or a small roller. Wait 5 to 15 minutes to allow the first coat to soak into the grout. Start wiping the sealer off after 5 minutes. Allow the grout sealer to cure. Test the grout sealant.