I've been reading about Helen Keller in various places online, and there are frequent mentions of how she learned the words for things and how she learned to read braille, but I haven't seen anything about how she learned sentence structure and about abstract concepts.
For example how did she learn about the use and purpose of articles in a sentence? And how did she learn what religion is? (I saw a quote by her that mentioned something about religion, which is why I ask.)
This video actually shows Anne Sullivan, her teacher, and Helen Keller together describing the learning process. Once speech was established, Anne was able to read braille to Helen with one hand her face, and the other hand on the braille letters. As a result, Helen also learned how to write in braille as seen here.
One thing to keep in mind is that Anne could read books to her, and if a book had a braille translation, she could read that. As I'm not an expert on braille, I can't explain how she would understand the purpose of articles in a sentence. Phillips Brooks, a reverend, is believed to have taught her about Christianity.