CIL is a levy that local authorities can choose to charge on new developments in their area. The money should be used to support development by funding infrastructure that the council, local community and neighbourhoods want.
CIL regulations have changed the developer payment landscape by introducing the levy and also by changing when councils can seek s106 obligations. Developer payments contribute to the provision of infrastructure or refurbishment of existing provision to support the additional burden new development makes on both local and strategic infrastructure.
To understand how it works please see the Planning Practice Guidance on CIL.