If you want to buy a better weapon or get a fancy mount, you will need gil. You can earn gil in a variety of ways, including selling items to other players on the Market Board. You can also make gil by killing monsters. The best time to sell is around major patch updates, when more players are buying. However, the in-game economy is volatile and nothing is guaranteed.
It is the main currency...
Arabic
French
Spanish
Portuguese
Deutsch
Turkish
Dutch
Italiano
Russian
Romaian
Portuguese (Brazil)
Greek