Player Guilds are associations of Players/Characters that form their own guild. Factions are not the same as Guilds. Factions are Knights of Solamnia, Wizards of High Sorcery, Dragon Army, etc.
Guilds can create & share guild vaults, purchase a guild house, have a guild merchant (Sells items as a merchant and adds proceeds to guild vault), purchase guild branches (for selling item from Guilds Merchant & Accessing guild vault around world), create their own ranking & naming system, their own respawn location, as well as several other features.
To start a guild as a guild master, a character must meet the following requirements:
Level 40.
Charisma of 18 or Greater.
Intelligence of 18 or Greater.
10 Ranks in Persuade Skill.
Leadership Feat.
15,000 gold pieces.