Guild quests
Quests give Guild Points. Each member's points add to the guild total, which unlocks rewards. Quests come in weekly sets, and each has 6 stages. What they ask for and how many points they pay depends on the season. The Guild tab shows each member's share and the guild total.
Levels
Guilds earn XP and rise in level, and certain levels unlock Guild Perks.
Seasons
Each season has its own guild egg, such as the 
Season 1 Guild Egg.