FROM JAPAN, basically you have to paste the item's web address into the search bar and then fill out the form provided.
There's a comments box that lets you add more specific information, like which colour you're after. Though they recommend filling it out in Japanese.
I wanted the red "Original Brown" version, so I pasted "オリジナルブラウン" into the box. If you want the blue "Original Gray" version, it's "オリジナルグレー"
As for payment, that comes later. With FJ you have to pay a deposit which is then used to pay for the item and delivery.
EDIT: My mistake, turns out deposits are more for auctions.