Need help with using a/an/the

I have 2 different sentences: I saw___man in __ armchair at____window. He was reading_____newspaper. Then I saw ______woman in _____ garden house and knocked on her window and whispered: 'Please help me!' and I have some questions:1. The first sentence I put a/the/the/the or a/the/the/-. But I am not quit clear why I should put the 2 "the" there. So can I put a/a/a/a? and why?2. The second sentence I think I can put a/the and a/a. I prefer to use a/a. What do you think?3. Can someone introduce me a more sophisticated (difficult/confusing) examples? The grammar books/ebooks that I have only introduce some simple rules with simple single sentences.Thanks!