The pedagogical approach is anchored in formal definitions/proof of security, but in a way that I believe is more accessible than what is "traditional" in crypto. All security definitions are written in a unified and simplified "game-based" style. For an example of what security definitions look like in this style, see the index of security definitions (which will make more sense after reading chapters 2 & 4).
This video introduces basic terminology in cryptography, including what is a ciphertext, plaintext, keys, public key crypto, and private key crypto. This is a video shared via the picoCTF youtube channel. picoCTF is a platform organized by Carnegie Mellon University (“CMU”)