Every tattoo hurts,but they are varying in discomfort by person and location.
General rules of thumb:
If it can feel good it can feel real bad.
\"Fleshy\" areas hurt less than \"boney\" areas.
Bendy parts suck.
Outside skin is less painful than inside skin.
Anywhere that is typically exposed to weather and sun will be less painful than typically covered skin.
Nerve clusters can be horrible or dull depending on the person.
Anywhere that you see a blue line is going to be more painful than an area without one.Back pieces can feel more extreme because you can't see the needle.
Being hydrated and fueled will reduce the pain,but will increase bloodflow and immune response to the tattoo wound.
As for what a tattoo feels like,it varies from a slight scraping like sandpaper to an extreme burning and puncture like you are being tapped with a glove that has a hot thumbtack through the finger.Sometimes it feels like that thumbtack is being inserted and then dragged across your skin.Sometimes with color shading it feels like you are getting a cheese grater pulled over just the top layer of your skin.
If it's in a nerve ending like your elbow you can feel it in your jaw vibrating.It's all relative to your person though and how you are wired,you won't know until you hit it.