Only guild leader and officers can attack other guilds. Attack lasts 24 hours.
You can attack any guild member by clicking "Attack" button in your Guild Screen. You can attack 9 opponents at your choice in first attack slot, 8 opponents in second attack slot and 7 in third slot. You cannot attack same opponent twice until cooldown is over (time to time a bug appears allowing you to attack same opponent again).
For victory you receive guild wars points (points depend on opponent's AP), half of this points lose opponent. But if you have attacked player and lost the fight then you lose points and your opponent gain points.
If you kick guild member with negative guild wars points it won't increase total points your guild earned in guild wars.
You receive Fire Crystals every sunday at 00:00 UTC/GMT +3
(TOP 1 guild gets 100 Fire Crystals, TOP 2 — 75, TOP 3 — 60 etc.)
Fire Crystals can be used to summon in Guilds Crypt x5
Fire Crystals is a currency, that doesn't take slot in your army. You can check how much Fire Crystals you have by clicking "Raids" button in Guild Screen or by clicking "Summon" button and then "Premium" in main screen.