The main difference between a tuxedo and a suit is that a tuxedo has satin on the pocket trim, buttons and lapels. They also have satin stripes down the trouser legs. Suits do not have any satin.
Suits are typically worn with a long tie, while tuxedos are worn with a bow tie and a cummerbund or vest. Tuxedos are frequently worn by grooms at weddings as a more formal choice than a suit. Suits can be worn in the workplace, but it would be out of place for a tuxedo to be anywhere besides a formal event or a wedding.