Different Ciphers (will add more later)

The Caesar cipher:

 involves shifting around the value or start point of the letters of the alphabet, for example: If normally A=0 B=1 C=2 I could instead start the alphabet at X=0 Y=1 Z=2 and it would loop back around to A=3 B=4 C=5 until we reach all 25. This would make the key for deciphering the code 23 because we moved 23 spaces from the original starting number.

So the cipher "zxq" can be decoded with the key "23" by counting back in the normal alphabet 23 spaces so Z=C X=A and G=T so the message we decoded was "cat"

You can change around the starting point or the number of spaces any way you want to create a new key for the cipher and create your own codes! this is maybe the easiest cipher out there to use that requires a key!

The Atbash cipher:

 This is also a incredibly simple cipher if not more so

 you just mirror the alphabet so A=Z B=Y C=X there's really no key or anything here other than mirroring the start and end of the alphabet together.

so "cat" put through this cipher would be "xzg"

The A1Z26 cipher: 

Also incredibly easy, 

you just replace the letters with their number value or place in the normal English alphabet.

 so say I wanted to to put the word "secret" through the cipher, it would give me "19-5-3-18-5-20". 

The Vigenere cipher: (to add later)