Guilds are groups of players in Helmet Heroes, which can be formed or joined in Mushroom Village. Creating a guild costs $200,000.
When you slay a monster, the experience is divided between the guild members sharing the same stage, with non-integer amounts of experience rounded up. Between two players, the slayer receives 62.666% of the XP, while the other member recieves 37.333% of the XP from a slain monster (it is currently unknown how this divides up between three or more players).
As of Patch 2.51, Guilds are now able to engage in Guild vs. Guild Combat in the PvP Arena. Players can enter the GVP Woodlands with fellow Guild members, and team up against players from other Guilds, without harming fellow Guild Members in combat.
Every player in a guild has a contribution score, which is a rough measure of how much they have helped the guild. When you kill a monster when guildmates are in the same area as you, you gain contribution equal to the number of experience points they received. Kills in the GvG area give 5 contribution apiece as well.
Guild Wiki Page
Anybody with a guild is allowed to create a wiki page for their guild. The address should be <Guild_Name> (Guild), and it should be under the Guild category (if it isn't categorized, then other players won't be able to find it)