Could you recommend me a resource on study of number systems?

Question

I tried to find some recourse on the Internet about number systems. I'd like to know about conversions between different number systems and operations with numbers within them. I tried to find it but there's only tutorials on different methods of how to convert and etc without real explanation of why it is done like that and not some other way but the latter is exactly what I'd like to know. Could you tell me where I can find what I am looking for? May be a book or a website. Sorry if this sounds a little "wavy", I'm novice here. Studying computer science and love math. Just trying to really understand. Thank you really much. (about myself, I do not have a big experience with algorithms. I am not some cool "math-guy". I started with math only recently and by the time I do not even know the very basics of calculus.)