What is the job of a left midfielder in Football?

This would depend on two things a) the formation the football team play in 4-4-2 the left midfeild should both provide cover for the left back and crosses to the forwards. 5-3-2 the job would be more link play between defence and forward link and getting forward as much as possible. 3-5-2 the left midefeild would be a wing-back, this means playing as a full-back which providing width down the wings. b) The tactics the coach wants to play - It's the job of each player to follow the the instructions of the coach and the midfeild area is where any instructions should be followed to the lettter. You could be asked to play attacking midfeild where you support the front palyers as often as possible (Ryan Giggs) holding Midfield where it's your job to maintaince a presence and get the ball then pass it on (Kewne) and given a free role. Nost time the role would depend on the coach. Hope that helps.
they are pretty much in charge of the whole field because they have to go back and fourth and they can score goals. (but they aren't supposed to go in front of the forwards) and they also have to help on defence too.