http://www.guildwars2hub.com/guides/...guild-missions
SUMMARY
*Guild Missions become available after your guild has upgraded the four categories within the guild panel, to a certain level.
*Guild Missions cost 50,000 Influence to unlock and 200 influence to activate.
*Higher tiered Guild Missions can be purchased with further influence and Merits (awarded from completing Guild Missions.)
*Merits are awarded on a tiered basis and are a natural limiting factor due to how many you can earn in a week, preventing large guilds unlocking all tiers instantly from influence they may have stored.
*2 Commendations are awarded to each individual who completes a guild event and can be traded for items from the new vendor in Lions Arch.
*Further rewards for completing a Guild Mission include two rare items or higher and 50 silver.
*Precursors are part of the reward loot table for completing a Guild Mission.
*Having World Completion is a huge benefit when participating in most of the Guild
Missions as Waypointing quickly to far flung locations is a must.
*Working together is paramount to successfully completing Guild Missions, as without it you will fail.