you can add gems only to crafted weapons, armors and accessories, and btw there are not many good things you can craft, and to be able to craft those items you need to get the receipes in dungeons or raids. basically, it's a lot easier to collect some gold and buy them at the trader, especially since, if you reach lvl 80 without shortcuts, you should get more or less 20 gold in the process...
moreover, if you want to buy the expansion, the easiest path is: once you reach lvl80, buy a cheap blue equipment at trader, thend decide which khitai factions you prefere, then go to northern grassland and start questing for them, to get marks of acclaim and gold, then buy one of their blue sets...
in the meantime, everytime you have the chance, join normal mode groups, old world dungeons groups and t1/t2 raids...
once you have some experience and the required alternate advancement abilities, start to join hardmodes...
it will take some time to progress, and it may look rather slow at the beginning, just don't get discouraged, and you'll get your rewards, both in terms of gear and fun...
one thing that will help you a lot is to join a guild, that can teach you the tactics and help you to progress...