A famous example of a deaf/blind person is https://en.wikipedia.org/wiki/Helen_Keller - this article contains some explanations about how she was able to learn to communicate with the world.
I have actually dealt with a partial deaf blind student back in elementary school.
You can sign ASL into their hand so they can feel what you're signing(normally individual letters). Or they hold your hands to feel the gesture/sign you're are making.