Simple Caesar Cipher Function
Just some things that jump out at me:

Standard VBA Naming conventions have camelCase for local variables, and PascalCase only for sub/function names and Module/Global Variables. This allows you to tell at a glance if the variable you're looking at is local to your procedure, or coming from somewhere else.



I would probably use EncryptUsingCaesarCypher as your function name. It's more descriptive and closer to what it actually does.

`Text = CaesarCypher(text)


versus

`Text = EncryptUsingCaesarCypher(text)


Other than that, your naming is pretty solid.



Why separate functions for ShiftLeft and ShiftRight? The code in both is heavily-repeated and could be easily combined into a Shift(ByVal shiftValue as Long) function that handles positive and negative. This also lets you cut out all that messing around with isPositve and Abs(shift)