The first thing you want to do is to get a feel of the tattoo gun before you start working. That will give you the confidence to start the tattooing process. Plug one end to the power mains and the other end of the power cord into the foot pedal. The foot pedal supplies the tattoo gun with power when the pedal is depressed and then cuts the power when you let off of the pedal. So the starting and stopping of the tattoo gun is controlled by your feet.
Another cord runs out from the pedal which you will plug into your tattoo gun when you are prepared to ink the tattoo design. Always be very cautious when handling the tattoo gun and do not plug it in until you are ready, you may hurt the customer or even yourself if you accidentally hit the pedal. But the steadiness will improve with practice, just like the dentist with his drill.
Next, select a suitable needle and attach it to the tattoo machine. The needle will be attached to a tightening screw on top of the gun and tightened down. Get ready the tattoo ink. The most convenient way to work is to pour a little bit of the ink into the plastic lid and set it on the work bench to use as needed. Just like how you would paint with a brush, dip the needle that is in the tattoo gun into the tattoo ink. Step down on the pedal to get the needle moving.
Some word of caution here: Always work only when your hand is steady and always use clean tattoo supplies. Use only sterilized needles. Tattoo needles will come in plastic wrappers that keep the needles sterile and needs to be disposed of when the tattoo job is done.