Once you’ve put down your stain and you’ve done the proper cleanup it’s time to seal your concrete.  Sealers provide long term protection as well as color enhancement. 
    For exterior applications you will most likely want to use an acrylic sealer to allow moisture in the slab to escape.  When used outdoors a solvent based acrylic sealer will generally perform better than water based.  You can use a silicone based sealer if you are trying to avoid a wet or shiny look.  
    For interior applications the primary types of sealers are acrylics, urethanes, and epoxies. Acrylics are UV stable, inexpensive, and easy to apply, but they are soft and require the most maintenance.  These provide a glossy look that really enhances the appearance of colored finishes.  As previously stated, there are both solvent-based and water-based acrylic sealers.  When applying indoors some contractors prefer to put down one coat of solvent based acrylic sealer followed by a topcoat application of water based acrylic.  This makes maintenance as easy as applying another coat of water-based acrylic sealer or wax once every 2-3 years.  
    Epoxy based sealers are much harder than acrylics.  Water based epoxies bond well to concrete and provide a clear finish.  Unlike acrylics, epoxies are non-porous and will not allow moisture to escape.  These factors make epoxy sealers the best choice for concrete countertops and food preparation areas.  They are not UV resistant so they cannot be used outside.  Also, reapplying epoxy sealers requires much more elaborate preparation than acrylics.  
    Urethane sealers provide the most scratch resistant surface of the three.  Unfortunately they are also the most costly.  Urethane sealers have trouble bonding to concrete and must be applied over water-based epoxy applications.  They are not UV-stable, and reapplication is expensive.