How is a factory reset done? So, I'm very new to Apple products and am feeling a bit naive about it all - so, forgive me if this sounds a bit stupid!

I am thinking about purchasing a used iPod touch 5th gen 64gb and I am wondering how a factory reset is done and if I can do it myself or if I would need to take it to a store. As well as how much does a reset do? Does it remove the previous user's junk?
If your buying a used iPod Touch whoever sold it to you will probably (and should) reset the device.   If its not or you just want to reset it you can do it by going into Settings > General > Reset > Erase all Content and Settings