Copy the code by highlighting it and holding the CTRL key while you click "C" on your keyboard.
At the top of this page, click on "My Profile"
On the next page, in the text box under the word "Signature," paste the code by holding down the CTRL key while you click "V" on your keyboard.
Click the button on the screen that says, "Update General Info" and your signature should then be under your posts.
Very cute little tool. :)