All tattoo equipment is not the same, not in quality, price or purpose. It is important to make sure you have the right tools before attempting something as permanent as a tattoo.
The parts of a tattoo machine are the frame with attached pieces, the tubes which can be removed for sterilization for each tattoo, and the needles that are inserted into the tubes and stick out the tubes opening at the end. The tubes also have a hand grip on them, which is where the tattoo artist holds the tattoo machine. These tubes are almost always stainless steel, with the hand grips the same, or a hard plastic. These tubes do not actually touch the customers skin, but ink and blood do come in contact with them, which is why they can be released from the rest of the machine and autoclaved. The tubes can come in many different sizes in relation to the tip where the needles are held being very small to extremely large. The tube end that connect to the tattoo machine is always the same size so that they are interchangeable.
There are two types of tattoo machines, a liner and a shader. These are pretty much dedicated to what their names imply, with little variation. There are minor differences in how they are built, with the liner having smaller coils, and a more upright position. The shader is made to be held a little more angled, and has larger coils.
The liner is used to hold only liner needles, which are needle bars with only small amounts of needles attached into a tight group at the end of the needle bar. The needles stick out of the tip of the tubes that attaches to the tattoo machine. The liner, as a machine, brings the needles up and down into the skin which perforates it, and deposits ink into the said perforations. It is used to do linework and small details. Most liners can handle needles as small as one needle, or as many as ten. The shader is used to fill in larger areas of skin, and needs the larger coils with more power to do so.
A power chord attaches to the tattoo machine and into a power source. This power source then plugs into an electric outlet (or in some rare occasions, a battery pack). The power source has a dial on it that allows the tattoo artist to adjust the amount of power that the tattoo machine gets. The power source also makes sure that the tattoo machine gets an even measure of power, so that the tattoo quality is consistent.
A foot pedal that stays on the ground also plugs into the power source. This is stepped on to make the tattoo machine run, and released to have it stop. It is just an on/off mechanism, though, and not pressure sensitive like a car gas pedal.
The needles are dipped into ink caps of the color desired. It is much like a paintbrush being dipped into the paint. When it is time to change colors, the tattoo needles are rinsed in a cup of water, and then re-dipped into the new color.