Can you use 40 amp breaker for your lights and plug ins?

If you are referring to house wiring then the answer is no. A breaker protects the wire size that is connected to the breaker. In home wiring most homes are wired with a #14 wire which is rated at 15 amps. That is why the wire is protected by a 15 amp breaker. The correct wire size to connect to a 40 amp breaker is a #8. This size wire is too large to connect to receptacles an light fixture terminals.