The Weapon/Armor Store is marked by the Sword on the mini-map in the top-right corner of your screen. It's located West (2D axis) of the Water Fountain, at the center of the Square. Merchant Chancy will be standing out front. You can buy a variety of equips here.
Clicking on an item will show, via a small version of your character in the lower-left corner of the shop, what you would look like if you equiped that item. You can see what each degree set looks like via the fashions that can be found in the character guides.