There you go; a link to the stages of dementia & what to expect. The others' suggestions for books to read and videos to watch address the 'how to handle' bit of your post.
"The 36 Hour Day" and "Learning to Speak Alzheimer's" are 2 excellent caregiver books that will answer your questions. The best thing you can do is to become educated about dementia symptoms and the diseases that cause dementia.
Pumpkin, can you provide more details or narrow down your question? Is your LO displaying certain behaviors at the moment? If so, which ones? Teepa Snow has some very educational videos on YouTube about dementia.
There you go; a link to the stages of dementia & what to expect. The others' suggestions for books to read and videos to watch address the 'how to handle' bit of your post.
Good luck