You always need to clean your pavers before you seal them as over time mold and mildew will accumulate on the pavers and this has to be removed before you can sand and seal them
Once you pressure wash your pavers you will need to sand the joints which will allow you to seal the sand when the paver itself gets sealer applied and weeds will not grow up out of the joints in between the pavers. Also the sealer will soak into the paver and seal it so no water will get down into the paver giving your paver a long lasting seal which will last outside 3 to 5 years.
You can get a gloss sealer or a natural sealer which will make them look like natural stone
