You can't download comics from cbr reader, but you download cbr files to read on it. I use getcomics.info or libgen.lc to download newer stuff or older stuff respectively, you could also use torrent sites. Note that this is illegal for a lot of comics including marvel and dc and you could be fined heavily by the government if caught, but you could just do it anyway if you feel like it. There are sites with legal cbr files such as comicbookplus.com but the books are 60+ years old and won't have many characters you've heard of before.