How do I set up and use custom fields?

I'VE CREATED A CUSTOM FIELD FOR EACH CONTACT. IT'S A SPECIFIC LINK TO A WEBSTORE CREATED FOR THEIR ORGANIZATION. IT'S SPECIFIC TO THEM. I'VE PLACED THE LINK IN THEIR CONTACT INFO AND NAMED IT "STORE LINK". WHEN I CREATE AN EMAIL AND INSERT THIS LINK IT DOES NOT APPEAR IN EMAILS. IT SHOWS {STORE LINK} BUT WHEN THE EMAIL IS SENT IT DOES NOT PULL IN THE CUSTOM FIELD. ANY IDEAS?