FYI: I don't have the profession, so any detailed questions may be better directed to those that actually have the skill. I'll do my best to answer whatever I can though.
A quick look through this link will give you an idea of what that gem you just found can be cut into.
http://www.thottbot.net/beta?gem=All
Here's another list of jewels by socket color and properties
http://www.wowwiki.com/Jewel
Below is a quick 0-300 Jewelcrafting guide and shopping list for those interested in powerleveling the skill.
120 copper bar
20 malachite
20 shadowgem
160 coarse stone
20 bronze bar (= 10 copper bar, 10 tin bar)
80 silver bar
15 jade
80 heavy stone
40 iron bar
70 gold bar
20 citrine
35 aquamarine
60 mithril bar
50 truesilver bar
45 star ruby
295 thorium bar
40 large opal
20 huge emerald
10 large fang
50 flask of mojo
20 powerful mojo
20 essence of earth
What to do:
skill 1-30ish: 60 delicate copper wire (needs: 120 copper bar)
skill 30ish-50: malachite pendant until skill 50 (needs: 1 malachite, 1 delicate copper wire each)
skill 50-70: 20 coarse stone statue (needs: 160 coarse stone)
skill 70-80: 10 elegant silver ring (needs: 20 silver bar)
skill 80-110: 30 ring of silver might (needs: 60 silver bar)
skill 110-120: 10 heavy stone statue (needs: 80 heavy stone)
skill 120-130: 10 ring of twilight shadows (needs: 20 shadowgem, 20 bronze bar)
skill 130-135: 5 barbaric iron collar (needs: 10 large fang, 40 iron bar, 10 delicate copper wire)
skill 135-150: 15 golden dragon ring (needs: 15 jade, 30 gold bar, 30 delicate copper wire)
skill 150-180: 30 mithril filigree (needs: 60 mithril bar)
skill 180-200: 20 engraved truesilver ring (needs: 40 gold bar, 20 truesilver bar)
skill 200-210: 10 truesilver commander's ring (needs: 30 truesilver bar, 20 star ruby, 20 citrine)
skill 210-220: 10 aquamarine signet (needs: 30 aquamarine, 40 flask of mojo)
skill 220-225: 5 aquamarine pendant of the warrior (needs: 5 aquamarine, 10 flask of mojo, 15 mithril filigree)
skill 225-235ish: 55 thorium setting (needs: 165 thorium bar)
skill 235ish-260: ruby pendant of fire until 260 (needs: 1 star ruby, 1 thorium setting each)
skill 260-280: 20 simple opal ring (needs: 40 large opal, 40 thorium bar, 20 thorium setting)
skill 280-290: 10 onslaught ring (needs: 20 powerful mojo, 20 essence of earth, 80 thorium bar)
skill 290-300: 10 emerald lion ring (needs: 20 huge emerald, 10 thorium bar, 10 thorium setting)