Council tax funds local services — refuse collection, street lighting, social care, libraries, policing. The annual bill depends on two things: the property's council-tax band (which reflects an estimated 1991 valuation in England) and the rate your local authority charges that band.
Single-occupier discount (25%) applies when only one adult lives in the property. Students, certain carers, and severely-mentally-impaired residents may be entirely exempt. Empty properties may attract a premium after a defined vacancy period.
For new builds the band is assigned by the Valuation Office Agency (VOA) within ~3 months of completion. You can appeal a banding within 6 months of moving in if comparable properties on the street are banded lower.