system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How did they teach Helen Keller advanced words/concepts?

I understand that her teacher was excellent and thought outside of the box, but if Helen Keller had no sight or hearing, how could they teach her the meaning of words like "is"? 
Every source I read gave a little history of where Helen went and who her teachers were, and there were lots of quotes from her writing, but I'm still not finding an explanation. 
In my understanding, teaching someone to communicate by signing in their hand would teach them basic words that they could feel, but even after many years, I feel like they would still be understanding in broken sentences, like being in a foreign country and asking for food or the bathroom just by knowing basic words, the sentences would only be "I need bathroom" and things like that. 

After reading all the resources I could find and not seeing a clear answer, I'm completely unashamed to ask this question. So, please share any information you know, and if this is a dumb question, I think I'm in the right subreddit, because clearly I need it broken down like I'm five!
gpt
The same way a baby learns language.  You start with basic words and build from there.  So simple words like water and cold are easy to teach and if as a teacher you continuously sign sentences like "water is cold" or "steam is hot" while putting her other hand in cold water or hot steam, eventually she will pick up the meanings of a word like "is."