The basic principle of Caesars Cipher is: Whatever the regular message contains you replace each letter with a letter shifted by a certain amount. Julius Caesar would use this method to encrypt messages.
Symmetric Encryption: The same key is used to encrypt and decrypt and can be used to encrypt files on a disk or data in transit. Asymmetric Encryption: Uses a public and private key, one for encrypting and the other for decrypting. Asymmetric Encryption is mostly used for digital signatures and securing channels through something that might not be secure.
Computers generate random numbers with True Random Number Generation (TRNG) which generates numbers completely randomly(they don’t have a sequence) and are used for key generation. Computers can also use Pseudo-Random Number Generation(PRNG): which produces a sequence of numbers that eventually repeat and are used for more general cryptography and testing.
Encryption is securing whatever message or data and decrypting is unpacking it. An analogy is locking a door(encryption) and unlocking the door(decryption)