In a blog post on the official site today, one interestingly timed to coincide with a big launch going on today and tomorrow (ahem), Blizzard officially announced the start of the World of Warcraft Warlords of Draenor alpha test. The studio cautions players that not all of the promised content is in the alpha client, so don't panic when dataminers can't give you all the nitty-gritty on garrisons. They're not in yet.
Players interested in signing up for later phases of testing are instructed to create a beta profile on Battle.net. Applicants will be selected randomly.