Locate the main electrical shut-off. Your house may be equipped with fuses or circuit breakers.

If your house has fuses, you will find a knife switch handle or pullout fuse that should be marked "MAIN."

If your house has circuit breakers, you may need to open the metal door of the breaker box to reveal the circuit breakers never remove the metal cover). The main circuit breaker should be clearly marked showing on and off positions.

Turn off all the small breakers first, then turn off the "main". If you have any subpanels adjacent to the main fuse, breaker panel, or in other parts of the house, (in an emergency) be safe and shut them off too. 

Shorts can sometimes develop to cause a circuit to bypass the breaker or fuse. 

Note: All responsible family members should be shown how to turn off utilities in case of an emergency. 
They need to know what the utilities look like in both on and off positions. 

Always treat electrical appliances and fixtures as if the power is on, even if you think you have it turned off!