Okay, so imagine you're in a library. A kithaab is like a library book, but instead of being written in English, it's written in Arabic. It's like a really special book because it's usually a religious book that Muslims use to learn and practice their faith.
Inside the kithaab there are a lot of words that are written in a special way called calligraphy. Calligraphy is like really fancy handwriting where the letters are drawn in a really beautiful and ornate way.
People who read the kithaab have to learn how to read and write Arabic so they can understand what it says. It's kind of like learning a secret code!
The kithaab is a really important part of the Muslim faith, and it's something that people really treasure and take good care of.