There are many different formations, or sets, teams use both on offense and defense. Some of the basic and most common and shown below. On offense, teams use different formations in certain situations. If they need to pass, offenses use more receivers. If they like to run they can use more blockers.
Teams select the best formation that suit their team's players.
On defense, team use formations to suit their needs. If they like to blitz and be aggressive they use more linebackers. If they think the offense is going to pass, they use more defensive backs. Below are some of the common formations, or sets, team use. Next time you watch football, see if you can identify the different ones by name.