Cryptograph means secret writing, in order to make information secret we use cipher, an algorithm that converts plain text to cipher-text. Cipher has been used long before computer existance.
In 44 BC Julius Caesar uses the technique now called Caeser Cipher to send message. He used to shfit the letter by 3 character.
Another great example from history, Nazis Enigma Machine used during war to translate message.
Data Encryption Standard (DES) is the first algorithm written for Cryptography in early 19th century.
A process of making text secret is called Encryption and the reverse process is called Decryption. So far the Cryptography technique we mentioned above relies on keys known by sender and receiver. Though manual sharing key is not good idea, solutions is to automate exchange of keys. We can do this by using one way functions, to understand one way function here is the Good example of one way function is Diffie-Hellman key exchange.
There are two types Encryption Symmetric encryption and Asymmetric encryption please follow the link for more details