Just like many other professions, there is a tool you have to purchase and keep with you: The "Jeweler's Kit" - sold by most of Trade Goods vendors for 8s - so you can easily throw it away and repurchase (I do this on my main with my Blacksmithing tools). You will need Simple Grinder for GEM cutting.
With Jewelcrafting you can produce rings, necklaces, trinkets, crowns and socketable gems. The last one is used for improving socketed items and it's new feature of TBC. Looking at the Jewelcrafting list makes one thing obvious - it can produce nice items for lower level chars. Many of produced items have nice stats and can be Jewlecrafting usefully up to level 30 (after level 30 the dungeons will provide better items). And end-game? Producing gems to improve socketed gear is something really, really good.
Your leveling of Jewelcrafting will need lot of mats. Good news is that up to level 300 you are fine with mats found in Old World, over 300 you will need mats found only in Outland. Your Jewelcrafting level is also involved in your possibility to use Prospecting (mining is still a must since you cannot Prospect non-base ores).
GEM cutting is another skill of Jewelcrafter - you simply get a gem, the appropriate recipe and Simple Grinder (Trade Goods from vendor). Meta gems have a cutting cooldown (1 hours) - There is NO cooldown when cutting Uncommon and Rare gems. And the different recipes allow you to perform different types of cuts (Brilliant, Gleaming, Thick, Rigit and Smooth) with different stats result.