You have to shift the letters in the alphabet for each letter. The number of letters you shift is different for each answer though.
For instance 4d answer parses to WEAR
To input this you need a crosser solved first.
The last letter of 7a is an A
So now comapare the A of 7 across with the "E" of Wear
The alphabet shifts 4 letters backwards
E becomes A
Therefore W - 4 letters = S
A - 4 letters = W
R - 4 letters = N
Therefore the input = SAWN
WEAR becomes SAWN for input
Every word coded and input is a legitimate word, but the number of letters you have to shift is not always 4. It can be 2, 1, 10, 8 whatever,