To buy a house, you need to have a VIP account and you need to be level 30 as minimum.
Firstly find a house without owner using ctrl+tab to locate on the map, an icon will appear on the empty houses, 'look' the door of the house to check and know the price, then stand facing the door of the house and then type !buyhouse.
Every month will be charged the price of the house from your depot, otherwise you will lose your house (the items are shipped to the depot automatically). To view informations about renting type !houseinfo.
The homeowner has many commands:
!invite - To invite someone to your house.
!viceowner - To set a second owner for the house
!door - To define who can open and close a certain door (stand facing the door you want).
!housekick player - To kick the person out of your house.
!sellhouse player - To sell the house for any players.
!leavehouse - To leave your home.