One of the reasons tubeless works so well in both road and mountain has to do with this magical product. In short, Stan's sealant makes running tubeless super reliable. The milky-white Stan's liquid coats the inner casing of the tire creating a latex-like seal while the excess liquid travels around the tire while the wheel is spinning to seal any holes or punctures in the casing from the outside world. Keep in mind, as wonderful as Stan's sealant is, it will dry up after a few months and need a refill every once in a while.
Installation can take place in one of two ways. The original way, which is to install one tire bead completely, then the other bead almost all the way, pour in a few cups of sealant, close the bead, air up and spin. The other way is to use the Stan's Tire Sealant Injector. With this tool, you simply install the tire, air it up (sans liquid) and seat the bead, then remove the valve core and un-air the tire. Screw on the injector and insert sealant through the valve, reinstall valve core and air up tire and spin. Either way is dead simple and effective. While Stan's is primarily used for tubeless wheels, it has also been known to breathe life back into flatted tubulars. In this case, you would use the injector method to seal up the inner tube of the tubular.
A handy fill cup and pour lid is included. One Quart 32oz will fill approximately 16 tires. Remember, Stan's will not freeze or degrade, so storage for long periods over winter months in your garage is not a problem. Shake well before use.