the operator's function is to act as a regulatory element that helps control the expression of the lac operon in response to the presence or absence of lactose. 2 setences

The operator in the lac operon serves as a binding site for the repressor protein, which inhibits transcription when lactose is not present. In the presence of lactose, the repressor is inactivated, allowing RNA polymerase to bind to the promoter and initiate transcription of the genes needed for lactose metabolism.