Buying a freehold property means that the property and the land on which it stands will be fully owned by you as the purchaser.  Houses are usually freehold. A service charge or ground rent is not usually payable unless you are sharing services or facilities (for example a shared driveway) with other property owners.
Buying a leasehold property means that your right to hold or use the property is granted by the freeholder under a lease for a fixed number of years.  Flats are usually leasehold.  Ground rent on the lease is paid annually by the leaseholder to the freeholder. A service charge is also often payable.  This is the contribution determined by and paid to the freeholder towards the cost of maintaining the building and/or estate that the property is in.  Often the freeholder will employ a management company to manage the day to day running of the building on its behalf, which will include the collection of ground rent and service charge.  The freeholder’s prior consent will usually be required for any alterations you wish to carry out to the property.