I recommend Bruce Schneier's Practical Cryptography (now renamed Cryptography Engineering in its second edition): https://www.schneier.com/books/practical-cryptography/

It's not a light read, but does provide a thorough introduction to the key concepts -- threat models, public-key encryption, digital signatures, etc -- and how they are applied.

It also compares the most popular 2-way encryption (AES, DES, etc) and hash (MD5, SHA, etc) algorithms.

Good stuff! I read it ... 20 years ago, and it provided much of the foundation I use professionally every day.