There are different staff members types. Most of them increase the amount of available trainings or healing sessions for your tennis player. The more staff members you have, the more you will be able to use different sessions to increase targeted characteristics or improve recovery. Careful, trainings cannot improve your characteristics above a given limit, which is defined by the level of your staff (=stars). It is thus necessary to hire better staff members to keep progressing.
An agent has a specific role by allowing to get new sponsors.

One of my staff members has a specialty, what does it mean?
Some staff members have specialties, it is a specific effect that other staff members don’t have. It increases the chances by 50% to progress on the specific characteristic targeted at the end of a tournament.

What is the time period next to each staff member?
When you hire a staff member, he is linked to your current coached player by a fixed-term contract, in number of tournaments/weeks. After this time, you will have to hire a new staff member of the same type.
If you decide to replace your current player by a new one, all his staff members will leave. You get back 50% of the invested amount.