Smithing is a craft that primarily deals with metals, weapons, and heavy armor. It is the only guild to have two full fledged guilds and can be joined by talking to the Guildmasters Mevreauche (North San d'Oria, E-6) or Ghemp (Bastok Metalworks, E-7). There is a smaller guild located in Al Zahbi.

You will need to speak to Mevreauche or Ghemp to advance in rank. He will request a test item. Trade it to him and he will grant you a new rank. You can take the test as soon as you acquire 8 skill points in your current ranking. (i.e. 8, 18, 28, 38, etc.)

Smithing materials are listed on the Auction House under the category Materials > Smithing . There are several NPCs in the Guild that will sell you certain materials for a reasonable price. There are five Smithing vendors in Vana'diel and they are open from 8:00 to 23:00. Watersday is the shop's weekly holiday.

Each guild has a Guildworker's Union Representative that will accept a certain item each day in exchange for "Guild Points". You may use these points to purchase special items and key item abilities. Speak to the Union Representative to sign a contract. You may only have a contract with one guild and signing a different contract will cause you to forfeit any guild points acquired from another guild. Additional points may be granted for high quality versions of the item. There is a limit to how many points you can acquire from a particular item.

The Guildworker's Union Representatives for the Smithing Guild are:

Lorena, Metalworks (F-7)
Macuillie, North San d'Oria (E-6)