The character creation screen class armor sets were originally added in Mists of Pandaria to preview what a class may look like once it was leveled up. The problem is that they were never actually made available in the game. This is finally changing in Warlords of Draenor. If you build a Salvage Yard in your garrison and upgrade it to level 3, the salvage crates you receive from missions have a chance to contain this armor. The crates can also contain some new weapon transmogs.
Simply load up WoW and create a new character to preview what the armor looks like, or check out the sets in the Wowhead model viewer. The monk and hunter shoulders are invisible, but it looks like those specific pieces will not be eligible for transmog. You can only loot armor for your own class.
The Salvage Yard takes up one of 3 small building plots in your garrison. Salvage crates can also contain upgraded gear for your followers, herbs, ore, and other items.