Answer:
Talk to the non-player character whose occupation is a guild registrar. These can be found in most major cities. Those being Shing Jea Monastary, Kaineng Center, Kamadan, Jewel of Istan, Lion's Arch and Ascalon City (Both post and pre-searing). Creating a guild requires a fee of one hundred gold coins.
You also have to select a name that meets a few requirements. Those being that it has to be two or more words long, it must be under 32 characters long, it cannot contain any language that may be found offensive, and the name cannot be already in usage by another guild.
Also, you'll be required to select a guild tag, between two and four characters long. The guild tag is not required to be unique, but once again, you are not allowed to use anything that may be found to be offensive.