Greetings,
All your tailoring and other tradeskill needs will be answered at www.eqtraders.com - It's a superb tradeskill website, and there are guides there to getting started on all trades.
I'm not sure what gems you're on about - there are some used in cultural tailoring (I'm a wood elf, so I use emeralds and blue diamonds). Gems are used in the leather armour quests in both Kael and Thurgadin, but those are quested (handed in to the NPC involved), rather than sewn.
Hope this helps, but post another question if I've missed the point of your original post!