With a tattoo, ink is transported under your skin with fine needles . This is a kind of art which is thousands of years old and still is very popular.
Although tattoos had a bad touch in the past, today it becomes some kind of art for the body. This was possible because of new ink, smaller and better needles and of course due to the new guns.
Of course one important things for a tattoo is the motive. Once a tattoo is finished it is very expensive and painfull to remove it.
So the best advice I can give you: Be sure what motive or kind of tattoo you want.