To make a guild, the very 1st requirement is to have your character be level 16 and learn the first level of the Leadership skill in your skill menu.

Next, select a town to have your guild base to be established. It is important because where you have your guild base let's you be able to control a Town in siege War.

Last, talk to the Officer NPC at the Town you want to have your guild base in. Select "Guild" option and click "Create Guild", enter guild name and your guild is now established in that particular town