Service charges cover your share of the cost of maintaining the building you live in or for shared services or areas. They usually cover things like cleaning and shared amenities such as sewerage services and communal gardens. The specifics of what you pay for will be set out in your annual statement. This is the only manageable way to share the costs of looking after these. They are normally paid monthly with the cost spread across the year.
If you are a shared owner these charges will be in addition to the monthly rent for the un-owned share of the property. You will also have a monthly charge for insurance, management and general services that you and other residents benefit from (such as looking after any shared areas).
If you are a Leaseholder this may only include shared sewerage service charges.