Deleted

How to get it?

it's a collector's item since (obviously) trading cards have already been released, leave it in your inventory

I have two of them and tried adding one to my game library but it did nothing

That gift was some kind of invitation, you can send to someone as a gift, when u activated it, u join to the Trading Cards Beta group, i still have Steam Trading Card Beta (Gift) and Steam Community Beta Access (Gift), when u try to Add to Your Game Library sure this message will show:

-This game is already in your game library.

The beta's are over, so the Trading Card Beta badge cant be earn, even if u have or buy (dont buy is a waste) one of this items.
(http://forums.steampowered.com/forums/showthread.php?t=3141374)
Q: Possible to get beta tester badge?
A: No.
(http://steamcommunity.com/groups/tradingcards/discussions/1/864973123626760888/)