I'm not a professional mathematician nor a skilled amateur mathematician, but I have interest in knowing what is the purpose of some mathematical subjects in a simple and clear way, accessible to a layman. (eg: Clifford A. Pickover's books). Can I ask such a thing on MSE?
Sure, but try to keep your questions focused. If a reasonable answer to your question would consist of a book, you're asking for too much. If a reasonable answer to your question would consist of a Wikipedia article, you should at least read the Wikipedia article first and ask questions about whatever's unclear in it.