I want to take a picture of my eye, how can I do that?

I have a Nikon D3100 camera. I would like to take a picture of my own eye with it. Can you please give me tips of how I can it?

Hold the camera towards your eye and push the button.
pretty simple

Put in close to your eye and press the button. I suggest to turn of the flash if you don't want to blind yourself lol

If you want a decent image, then your best bet is to buy a macro lens & get someone else to take it.