Football (soccer in America) has a few positions. Teams of 11 are broken down into defense, midfield and attack; but the formations have specific positions. Coaches select various formations for their teams that include some of the following positions.
For example, let us start with the goalkeeper, who is not regarded as a defender. This is the only position whereby the player can handle the ball in defense of their goal. They stand firm in the goal. As such, they can handle the ball within their penalty box and stop shots. It is worth noting, however, that goalkeepers can move further outfield for set-piece play or even to take a penalty and score a goal!
Outfield players defending the goal are defenders. Center backs (or central defenders) are those defenders who play more centrally within the penalty box. Full-back are defenders who play wider and push further forward more. Then you can also have a sweeper in a team who drops back very deep. For these players, winning the ball back is more often required.
The midfielders play in the middle. In the midfield there are a few variations. In a 4-4-2 there are two central midfielders who play in the center. These can actually be more defensive or attacking midfield players. Defensive midfielders may drop back a bit, while attacking midfielders will push further forward to support the forwards and possibly even score.
There are two midfielders who can play wider in the midfield. These players are the wingers. The winger actually supports the forwards a little more from the left and right side of the field. Wing-backs are actually more defensive wide-midfield players who may drop back a bit to defend.
The attack includes those positions that are furthest forward on the field and include players who score the most goals. A striker plays furthest forward and usually scores the most goals for a team. Other forward players (the forwards) may drop back a little. They can support the striker and score goals for the team themselves.
More versatile players may well be able to play in various positions. For example, an attacking midfielder might be able to start as a forward further up the field. Alternatively, other midfield players can perhaps drop back into a defensive position.
So there are variations on the defenders, midfield and attack positions in a soccer team. From the goalkeeper, central defenders, full-backs, wingers, central midfield players, forwards and strikers are all playing positions. All soccer formations will include at least a few of those playing positions.