So I lost 2 of my brake pins (the little plastic clear things) on my reel and I don't know what it means. Does that mean the brakes are on or off? And is there any way I can buy more of these little pins?

If they just slide u maybe able to cut the little tubes that come with the spray cans like wd 40,liquid wrench etc i know some are smaller then others and getting the right inside diameter and length is trial and error.

So if the plastic piece is completely off, is the brake on or off?

The brake should be off since the plastic piece is no longer there to cause any friction to slow the spool down. One of our more experienced reel techs may correct me but I believe that should be the case. 

bluebasser is right. Normally when these pins are not locked in, centrifugal force from the spool spinning forces them out and against the brake ring to cause friction and slow the spool. If there are no pins there, there's nothing to cause friction.

That's right. Those plastic tabs are brake shoes. No shoe / no friction / no braking. Unless you run all the brakes on, missing 1 or 2 won'y affect fishability at all. Academy should be able to put you in contact with the source for parts. I'm not sure who manufactures those. Silstar maybe. 

Ok thank you guys that was really helpful

If you're missing only two you should be OK. I only use 2 after getting used to my reels. I start with 3, then practice.

I have an express mettle bait caster. When I cast the thumb bar doesn’t lock when I turn the handle. It just spins and the thumb bar doesn’t click. I can lift it with my thumb and continue to fish. Is this worth fixing?

Deep clean and lube should correct that issue.