Worked example.

Decipher the following message, for which the key is

ROYALTY

TNGTH CYIIL XHEIH PANCA AXHGR OUFOA EMITE LSOIP INDSR
ROEAR ERANX EEEFT ILMSE AEANS CESON EX

1. Number the letters of the key in alphabetical order

   
   R O Y A L T Y
   4 3 6 1 2 5 7
   

2. There are 77 letters and the keyword is 7 long, so we need a 7*11 grid

      
   4
   3
   6
   1
   2
   5
   7
   

   For text editing reasons, 7 rows are easier than 7 columns.
3. Enter the first 11 letters into the row labeled 1

   
   4
   3 
   6
   1 TNGTHCYIILX
   2
   5
   7
   

4. Enter the next 11 letters into 2

   
   4
   3
   6
   1 TNGTHCYIILX
   2 HEIHPANCAAX
   5
   7
   

5. Enter the next 22 letters into 3 and 4

   
   4 TELSOIPINDS
   3 HGROUFOAEMI 
   6
   1 TNGTHCYIILX
   2 HEIHPANCAAX
   5
   7
   

6. and the remaining 33

   
   4 TELSOIPINDS
   3 HGROUFOAEMI 
   6 EEEFTILMSEA
   1 TNGTHCYIILX
   2 HEIHPANCAAX
   5 RROEARERANX 
   7 EANSCESONEX
   	    

7. To read off the message, read down the columns

   
   THE THREE GENERAL REGIONS OF THE SOUTH PACIFIC ARE 
   POLYNESIA MICRONESIA AND MELANESIA XXXX
   

   --------------------------------------------------

Your turn

Now do the same with this message, for which the key is

CREAMPUFF

HDUCP IEATL EIEUU OENOI XMMCI TATDF DSSHC HSSVS ISTAO
TRNGO HRSSG OHASF EMBLH FPEEO EE