hi

Your Loot Specialization is what chooses what gear bosses drop for you. To set it, follow these steps:

Step 1. Right click your Character Portrait
Step 2. Mouse over Loot Specialization
Step 3. Select the Specialization you want the boss to give you

If you want tanking loot, select Brewmaster.
If you want healing loot, select Mistweaver.
If you want damage loot, select Windwalker.

You might get one piece of gear or you might get gold. When the boss in LFR or Flex dies (or if you use a bonus roll) you have a chance to either get a piece of gear based off your Loot Specialization, or you may get a container of gold or other items.