Now i will talk to you about positions. There is 11 players allowed on the field at one time per team so there is always 22 players on the field. On offense There is the "main" man the quarterback he mainly throws but can run if needs be then their is the fullback his job is to either run or majoritely block for the running back then there is the halfback or running back who does what it says on the tin runs. Then there is the wide receivers who essentially run and try catch the ball and the tight ends who are a bigger version of the wide receivers e.g usually taller then 6'2. Then the underrated "blockers" left tackle, left guard, centre, right guard, right tackle there job is to block the defensive players (explained shortly) trying to either tackle the quarterback or running back.
Defense: Then their is the defense this a little less complicated first you have the defensive line made up of the defensive tackles and right and left ends their job is to get through the offensive blockers and sack (tackle) the quaterback or running back. Then there is the linebacker's. the middle linebackers job is (depending) on the play to either rush the quarterback as well (blitz) or drop back into coverage and try stop the pass getting to the wide receivers or tight ends then you have the outside linebackers they have a similar job to the middle linebacker but primarily work as extra defensive line players and help rush the quarterback. Then you have the cornerbacks who mark the wide receivers and try stop the pass. Then finally you have the safetys their job is primarily to stop the long pass or just help the cornerbacks mark the receivers.