#1 - Sept. 3, 2014, 2:56 a.m.
Blizzard Post
In the most recent beta build, Heroic dungeons may now be accessed through the Dungeon Finder (LFG) system. However, as will be the case in the live game, you must complete the Silver Proving Grounds challenge for a given role if you wish to queue for a level 100 Heroic dungeon as that role.

Next build there will be a regular garrison NPC that allows you to enter the Proving Grounds, but for testing, the Beta instance teleporter (Nexus-Lord Donjon Rade) should offer direct transport to the Proving Grounds. Tuning is not final, but please give the system a try, and post your feedback in this thread. (Then go queue for a Heroic dungeon and post your feedback in the appropriate dungeon thread!)