If someone drives your car, they are generally covered by your insurance. However, there are certain conditions and limitations.
Most policies include a "permissive use" clause, allowing occasional drivers to operate your vehicle with your explicit consent. Even if an unlisted driver uses your car, they can still drive covered. However, permissive use has limitations, such as frequency of use, excluded drivers and restrictions on business use.
Your car insurance primarily covers the car, not the driver, so if someone borrows your car with your permission, your insurance will be the primary coverage in an accident.