If you were to start one you would first have to chose what type of order you want. For example: Knights order, mercenary group, magic oriented guild and so on.
Then a HQ would have to be build or bought along with equipment relevant to the purpose of the guild/order.
Members would have to be recruited, either by persuading or "flyers" in public places, but of course in the start only some would be interested. As the fame of the guild/order grows more people want to join.
Profit from the guild/order would not come until it was rather succesful, but it could turn out to be either a economical master-piece or leave you with a rather large debt/loss of money.
If you don't like the guild/order you could disband it and try another type(?)
What do the forum think of this idea?