Now you need to collect all 5 of the mannequin parts. You can either get them from the source, or buy them from bazaars and through trades. They cannot be sold through the Auction House. Click on the link to find out how to get the part:
She will give you the mannequin that is the same Race and gender as your character. If you want a different mannequin then trade the one that you have back to Fyi Chalmwoh and she'll let you choose another one for 2,000 gil.
Once you've completed this quest, you will now be able to buy more mannequins from Fyi Chalmwoh for 100,000 gil each, or you can trade in one that you have to get one with a different race or gender.
To place equipment on the mannequin, put it in you Mog safe and arrange it like normal furniture. Then place the equipment you want to use in storage. Go back to layout, select the mannequin, press X, and select <Equip> from the menu. You can now equip the mannequin with the items in storage just as you would equip yourself with items in inventory. However, only equipment that is normally visible (Main, Sub, Range, Head, Body, Hands, Legs & Feet) can be used. Note that you will need to unequip an item before you can move out of storage. Also note that items still use up storage slots whether they are equipped or not.