G T Y O R J O T E O U I A B G T
Word puzzle hint: Try splitting the letters up into equal-sized groups.
This type of code is known as a Caesar Box because Julius Caesar was the first to write codes this way. To decipher the message, divide the code into four groups of four (you can also divide any message into groups such as 5 groups of 5 or 6 groups of 6 depending on the number of letters in the phrase), and rearrange them vertically like this:
G T Y O
R J O T
E O U I
A B G T
Then you read it vertically, column by column, left to right.