What's a record label for music and a "single" and a "B-side"?

A record label's job is to find music and acts that they think will sell really well, and then market/publicize the music in order to sell it at its max potential. One way they do that is by using a "single." A single is often the catchiest or most defining song of the album, it is meant to be very heavily publicized and marketed in order to hook people into learning more about the act and purchasing more music. It's almost like a commercial for the act. A B-Side track or single is like a bonus or incentive to buy the music. These days it goes by the name of "Bonus Track."