When a supply happens within a single state (an intra-state supply), GST is split into two equal components: CGST (Central GST), which goes to the central government, and SGST (State GST), which goes to the state government. For example, an 18% intra-state supply is billed as 9% CGST plus 9% SGST.
The split is automatic in correct billing software and is driven by the place-of-supply rules — not merely by where the seller is registered.