whenever i turn my ipod on the screen shows a picture of a charger, an arrow that points to itunes. what do i do next

Okay, I am not sure what type of generation my ipod touch is, I believe it is the 3rd generation., but whenever I go to turn it on, I shows a picture of the end of a charger (The part that plugs into a computer) and an arrow that points at the iTunes symbol. I have gone to iTunes, but I don't know what to do from there, please help me!!!