The player who receives the ball from the center at the start of each play before either handing it to the running back, throwing it to a receiver, or running with it himself.
The quarterback is usually the player in charge of running the offense on the field. He is also the guy that usually informs the offense of the play while in the huddle.
An offensive player who lines up in the backfield and generally is responsible for carrying the ball on run plays. A running back's primary role is to run with the football, he is also used as a receiver at times.
An offensive player who lines up in the offensive backfield and generally is responsible for run-blocking for the halfback and pass-blocking for the quarterback. Fullbacks are usually bigger than halfbacks, and also serve as short-yardage runners.
An offensive player who lines up on or near the line of scrimmage, but split to the outside. His primary job is to catch passes from the quarterback.
An offensive player who serves as a receiver and also a blocker. The tight end lines up beside the offensive tackle either to the right or to the left of the quarterback.
A member of the offensive line. There are two tackles on every play, and they line up on the outside of the offensive guards.
Offensive Guard A member of the offensive line. There are two guards on every play, and they line up on either side of the offensive center.
Center The offensive lineman who hikes (or snaps) the ball to the quarterback at the start of each play. The center lines up in the middle of the offensive line, between the offensive guards.