Locate Your Home's Main Water Shutoff Valve
Almost all homes have one main shutoff valve directly before the water meter and another directly after. Where the meter is located depends on the climate in your area. In cold climates, the meter and main shutoff valves are located inside, usually in a basement or other warm area to prevent freezing. In milder climates, the meter and its two shutoff valves may be attached to an exterior wall or nestled in an underground box with a removable lid.
Between the water main in the street and the meter, there's also usually a buried curb stop valve (accessible only by city workers wielding special long-handled wrenches) and a corporation stop, where your house water line hooks up to the water main. Your city absolutely doesn't want you messing around with these valves. Turn your water off or on using the main valve on the house side of the meter. This valve will normally be a gate-type valve, with a round knurled handle, requiring several full clockwise rotations to turn off. In newer homes, it could be a ball valve.
Find out more about main water shutoff valves here.
Locate the Electrical Panel
You'll usually find the main circuit breaker panel—a gray, metal box—in a utility room, garage or basement. Don't worry about opening the panel's door. All the dangerous stuff is behind another steel cover. Behind the door is the main breaker for the entire house (usually at the top of the panel) and two rows of other breakers below it, each controlling individual circuits. If you're lucky, there will be a guide that indicates which outlets and receptacles are served by each circuit.
Learn more about circuit breakers here.