This is All Things Store, if you click on any equip able item your character will try it out first and then if you like it, just press Take
and its yours. Some items are restricted by class or level. There are also some consumables you can buy, a notable among them is the Scroll of Escape
(a scroll with a green arrow) which returns you to the zone you bought it from. There are five different stores depending on the starting zone you are in, each contains its own inventory. The store in the imperial capital has three additional inventories Formal ,Jewelry and Special
(which is there for just fun).