If you want to learn how to use cryptography yourself, you'll want Bruce Schneier's marvelous _Applied Cryptography_ at some point. But if you want to find out what the fuss is about and what, exactly, cryptography has to do with information security, you'll find this introduction very, very helpful.
What's nice about it is that it not only gives you a fairly painless introduction to the essential concepts of cryptography, but also informs you in a reliable way about the importance of cryptographic protocols in electronic information exchange. It starts at the beginning _and_ gets you through to the meaty infosec stuff; even if you're an absolute beginner, by the time you reach the bits about e.g. digital certificates and public key cryptography and secure email and so forth, you'll actually be in a position to understand it.
Highly recommended to lawyers, law students, and other infosec newbies.