C is the "common" contact. It switches between the NO and the NC contacts.
NO is "normally open". The connection between it and C is OPEN then the relay coil is NOT powered.
NC is "normally closed". The connection between it and C is CLOSED then the relay coil is NOT powered.
When the relay is powered C disconnects from NC and connects to NO.
Those are the terminals at each end of the relay's coil. It appears that you are not familiar with electromechanical relays. This might help: **broken link removed**