Put briefly, the job of a coach is to improve the team's performance. A good coach will do whatever it takes to achieve this. This may involve working with all the team together or, at another time, talking to individual members; it can also involve working together with people and bodies outside the team.
A coach has to motivate, inspire and encourage. He or she must provide concrete ways that the team can keep developing, both all together and at the level of the individual player. The coach needs to know the strengths and weaknessed of each player and find the best position for them based on that knowledge; also to find ways of training and helping that person to build on their strengths and improve in other areas. A coach also has to step in when there is trouble and deal with it quickly, and to determine what the needs of the team are in all sorts of areas, eg training and equipment, to organise activities and much more.
You can find a good overview of a coach's job here.