Practical Cryptography by Bruce Schneier and Niels Ferguson is decent in that it gives a good lay of the land without diving too deep in to the mathematical rigor. The first half explains at a high level the concepts of encryption, key exchange, asymmetric encryption, digital signatures, and lays out the problem statement that PKI solves.

It's nice in that it will list out a bunch of available encryption algorithms or hash algorithms, but at the end of the chapter say "Just use this one, it's considered safe right now." i.e. AES256 and SHA256.

Unfortunately, it mostly avoids the practical steps of web security, like its not going to print out the command to type in to your shell to generate an SSL signing certificate. So I wouldn't recommend it if you're looking for an immediately practical book to help you secure your web server. But it orients you to the landscape so you have a general idea of what you're trying to achieve, and can google yourself the rest of the way there.