Everything will be heavily tied to your garrison in the new Warlords of Draenor expansion, and professions are no exception, you can't craft anything without your garrison. Below you will find explanation for the most important changes to the crafting system.

Profession skill level requirements removed

You can craft most new recipe from skill one. (skill requirements for old recipes remain unchanged) This is probably the biggest change, because you no longer have to spend thousands of gold to level your profession skill up. Your skill level now determines how many resource you get from doing your daily profession cooldown. There are some recipes for inscription and engineering that still requires 600 skill.

Work orders and daily cooldowns

Work orders and profession daily cooldowns convert raw materials like herbs and ores to a more useful reagent. Almost every new high level item you can craft requires this reagent generated from doing work orders, or your profession daily cooldwon, these reagents binds on pickup (except enchanting and alchemy).

• Work orders:

There are a lot of changes to professions in the new expansion, so I made this page to list what I gathered so far. I will update this page everytime I find something interesting in the new beta builds. Last update: november 1.

General changes

• Direct combat benefits of Professions will be removed. This means you no longer have to level professions to get 0.5% dps increase, so leveling a profession will be more like a personal choice now.
• Realm First profession achievements are gone.
• Work orders and profession daily cooldowns convert raw materials like herbs and ores to a more useful reagent. Almost every new item you can craft requires this reagent generated from doing work orders, or your profession daily cooldwon, these reagents binds on pickup.
• You can craft items at your garrison without having professions. But, you can't craft the best items, consumables.
• Herbalism, Mining and Skinning will be easier to level. You can now pick herbs, harvest mineral nodes and skin animals without a required skill. The amount of ore/herb/leather you'll get is determined by your skill level. This is similar what we have now for herbs and ores in pandaria. You can read more about this here.

There is an event called Darkmoon Faire that appears in the game once a month, starting at 00:01 on the Sunday before the 1st Monday of each month. During the event you can complete quests for each professions.

The profession quests can only be completed once during each Darkmoon Faire and will grant 5 skill points (means you can complete them again once at the next faire). 

The skillups will apply automatically to the most recent expansion profession progress that is not at its maximum. So, for example, if you want the +5 skill in Outland Engineering, but you have already learned other expansions profession skills, you have to max all of them out first, then you can get the +5 in Outland Engineering since that will be the only one that is not at its maximum.