As the term column transposition implies, this system uses columns to transpose the text of a message. The actual process is a bit confusing so it will be best explained by an example to illustrate the different steps.

The first step is to choose a keyword that is fairly long (6-10 characters) and can be easily remembered. Something like 'thinkquest' will work fairly well. The purpose of the keyword is really to just produce a long number. To create the number from the more easily remembered keyword, you find the letter in the word that comes first in the alphabet, and put a '1' over it. Then, you find the letter in the word that comes next in the alphabet and put a '2' over it. The following illustrates the method.

alphabet: abcdefghijklmnopqrstuvwxyz
keyword:   t h i n k q u e s t
keynumber: 8 2 3 5 4 6 0 1 7 9

The next step is to create a grid with the number of columns equal to the number of characters in the keyword ('thinkquest' has ten letters, so our grid will have ten columns). Each of these columns should be numbered according to their posisiton (first column = 1, second = 2...). Next, we create a row beneath the numbers and write the letters of the plaintext in the row, one letter per column. When the end of the row is reached, the message should continue in a new row beneath the old one. This process continues until the entire message is encoded. Several rows should be filled, as shown below. If the message doesn't completely fill the grid, nulls should be added to the beginning or end. The nulls will both fill the grid and confuse the cryptanalysist. But, in this case, we don't need any.

plaintext: history will be kind to me for i intend to write it - Winston Churchill

To produce the ciphertext, we first write down the key number created by our key word (ie: 8 2 3 5 4 6 0 1 7 9 from 'thinkquest'). We then take the first number, 8, and write the 8th column from the grid as the first part of our ciphertext. We then take the next number of the key number and use the corresponding column. The following example shows the work.

This process produces the nearly complete ciphertext. The only step left is to split the ciphertext into new word groupings so to mask the height of the columns. For our sake, we'll use 5 letters, which produces the following ciphertext.

plaintext: history will be kind to me for i intend to write it
ciphertext: wtte ibft seoo oiir tkrw rnii lmnt hled ydnt ioei
ciphertext (grouped): wttei bftse oooii rtkrw rniil mnthl edydn tioei

Now that you know the two basic processes (geometric/route and column), you're going to learn how to crack them.