From Black Desert Wiki
A guild is typically an in-game association of player characters. Guilds are formed to make grouping and raiding easier and more rewarding, as well as to form a social atmosphere in which to enjoy the game.
In Black desert there are three main type of guilds that can be created. They are the Military Guild, Merchant Guild, and Religious (Political Guild).
Military guilds have a purpose of battle. These guilds will fight for ownership of castles through Siege battles.
Merchant guilds are for earning money, exploring, and transporting goods through trade. No further information is known.
Religious guild is for getting familiar with many NPCs and chosen by election from NPCs. No further information is known.
After reaching level 40 speak to Lord Crucio Domongart in Serendia Hidel city.
No further information is known.