Making sure your multimeter leads are in the proper positions and that the multimeter is set to read amperage. Touch the negative lead of your multimeter (black) to the negative lead of your source (the battery in the picture below). Touch the positive lead of your multimeter (red) to the positive lead of your source. When the circuit is closed, or complete, the multimeter should give you a reading.
In this case, the battery is rated to provide a .5 Amp current, so the battery is working properly. Sometimes you get numbers that seem funky. Common issues are that you have your leads in the wrong place on your multimeter or you have not set your multimeter to read the proper AC or DC current.