How are people taught if they are born blind and deaf?
I can understand trying to teach someone via visuals or by talking to them but I can't figure out how you would teach someone multiplication or about government services or scammers without either.
Teach them tactile signs and go from there.
Watch The Miracle Worker for a notable famous example.
Helen Keller naturally came to my mind as well. She was not born blind and deaf though. She lost those sense at 19 months, so about a year and a half in. That is still quite young, but enough to establish the basis for things like object permanence and 3 dimensional space. In the climatic scene of The Miracle Worker, the main character says a word she learned as a baby, underscoring the importance of her early months.
To truly be born deaf and blind I think would be another degree more challenging.
I think the first step is generally establishing communication first. Like they might learn signs by touch. Later they could be taught braille in order to read.
A lot of times there are degrees of deafness or blindness. But one way to communicate is via touch: https://www.youtube.com/watch?v=9GrK3P15TYU