Plug the multimeter's black test lead cable into the "Common Terminal" jack on the front of the device. The black test lead cable represents the negative polarity; keep it plugged into the common jack at all times.
Plug the end of the red (positive) test lead cable into the "Amps" or "10A" input jack on the front of the multimeter. Use the "10A" input jack by default, although you can use the "Milliamps" input jack if testing currents smaller than 300mA.
Power on the multimeter and set its dial to the "Amps" or "A" section.
Turn the breaker off for the outlet or device you are testing. Most breaker boxes are labeled upon installation with the location or equipment each breaker provides current to. Disconnecting power before connecting the multimeter reduces the chance of shocking yourself, as well the possibility of damaging the device.
Connect the test probe lead wires. Insert the black (negative) test probe into the left outlet slot, and then the red (positive) lead into the right or "hot" slot.
Reconnect power to the breaker, then take the reading off the multimeter. The multimeter's screen will display the current in amperage increments.
Turn the breaker off once more and remove the multimeter's test probes from the outlet. Turn the breaker back on once you've finished removing the device completely.