How character-substitution encryption functions?

Character-substitution encryption works by replacing each character in the plaintext with a different character according to a specific system or key. This can involve a simple substitution, where each letter is replaced by another letter (like in the Caesar cipher), or a more complex method where a random permutation of the alphabet is used. The key is essential, as it dictates how characters are substituted, allowing for secure communication as long as the key remains secret. Decryption occurs by reversing the substitution process using the same key.