Defeated mobs will often drop loot, items that characters can add to their inventory. A blue and white briefcase icon indicates loot. Right-click the icon to open a loot bag and see the items available to loot. Right-click to loot individual items or use Shift + right-click to take all items in a bag.

Press V to automatically loot all the containers in your vicinity. A list of the items will appear in your chat window.