Encryption is the process of disguising information by transforming plain text into gibberish, otherwise known as cyphertext, which cannot be understood by unauthorized persons. Likewise, decryption is the process of transforming cyphertext back into plaintext that can be read by anyone. Examples of encryption can be found throughout history. In the cold war era, the Soviet Union and United States would send electronic messages from a specific military installation to another, but only on an encrypted basis. If the enemy intercepted the message, they would have to decypher the message in order to get the information. Typically when governments use encryption they use a very complex method of encrypting the data. Encryption doesn't have to be complex " the "Captain Video Decoder Rings" we had as children used a simplified encryption method. First, you'd encode your secret message, such as "Meet me by the swings," by replacing the letters of the alphabet with substitute letters from a from a specified position in the alphabet. Let's say we decide to use the key "+4"; using this method, we'd switch each letter in our message with the letter that comes four places later in the alphabet. D would become H; R would become V, and so on. By using this protocol, yourself or anyone you designate, can easily switch the H back to a D, the V back to an R, and figure out where to meet. These two examples are on opposite sides of the spectrum, but both have their similarities and their differences.
There are major differences in algorithmic complexity, the government pays mathematicians to research complex algorithms by which to encode the messages (like the system used by Captain Video) but these algorithms are complex enough that if you tried to crack them, it would take decades using the most powerful computers currently available. This complex mathematical code is what makes cyphertext unreadable to anyone who tries to crack it.