A winger plays on the sides of the field (there is a left and right winger), and often plays in crosses into the opposition's box. A winger plays defense, and also scores a good bit (Christiano Ronaldo often played winger the season he set the scoring record for the English Premier league).
Aspects of a Winger
A winger must be a good crosser, have high stamina, good dribbling skills, the ability to beat players, and good shooting. Only skilled players can take on this position.
Note that these are only primary aspects of a winger. They should be the strong points of a player who wants to play winger or is a winger. I can't stress enough how important it is to master all the aspects of soccer no matter what position you are playing.
Soccer Speed
Wingers are constantly beating players down the line and running after through balls. Speed is a necessity for wingers; you cannot be effective without it.
Dribbling Ability
The wing isn't crowded like the middle of the pitch, and therefore, more dribbling can be done. Wingers often have one-on-one encounters with other wingers, and it is necessary for one to be able to beat the other winger, and a defender too.
Endurance
A winger constantly moves back and force across the entire field and sprints often. Also, wingers perform tiresome tasks such as defending and taking on players. Therefore, a winger needs great stamina. If he doesn't have good stamina, he will have to be taken out.
Crossing Ability
Much of the time, the goal of a winger is to cross the ball. A winger must be a pretty good crosser, though they can get around this ability (through playing shorter passes instead of crossing the ball).
Defending Ability
As I mentioned before, wingers often face other wingers. Also, wingers must perform many of the tasks that defenders perform, such as sticking with a man, and defending crosses. For these reasons, a winger should be an adequate defender. The better he is at defending the better.
Winger Tips
Beat Your Man
Using the sidelines and your speed, you should be able to successfully beat your man. If not, get him of balance enough so that you can pass to the middle or send in a cross.
Master Stop-and-Start Moves
These moves are perfect for getting in a cross or for beating a man on the sidelines. A good winger executes these moves perfectly.
Cut Inside
Most defenders expect wingers to continue down the line. A quick cut to the inside often fakes defenders out and really opens up the field. When you cut inside, a center midfielder of defender has to pick you up, leaving a huge hole in the defense. From here, many options become available. You could beat the center man (which is usually easy considering he is probably to the side of you). You could execute a quick one-two with your fellow center midfielder. You could even cut in more and take a shot on goal!