When starting in your voluntary position it is always a good idea to agree what your roles and responsibilities are going to be.
As a volunteer you may only have a certain amount of time each week where you can perform your duties so it may also be useful to try and agree how many hours you are going to work and when these might be.
When joining a club it is likely that a current member of the club may act as a mentor to help you settle into your role, whilst some clubs may even have an induction process for new volunteers which will probably include things such as the organisation of the club, information on the facilities (toilets, changing rooms etc.) and health and safety issues.
If you have any questions or problems regarding your role you should talk with your clubs volunteer co-ordinator.