Now that you've got your house built and in working order, you'll need to start paying rent. Rent is due every 7 days from when the lot is purchased. You can check to see how much time you have remaining until your rent is due by right clicking on the outside of your house and then pressing the "Info" button located at the bottom of the interface window.
Paying your rent is pretty easy. Just click out the number of coins you want and then from the outside of the house click on the house itself. Beware, that once you deposit money into your house, it cannot be reclaimed. You can view how much coin you have in your house also by clicking on the Info button or by typing /house. Also notice that by pressing the "Info" button you can view the maximum amount of coin you can have stored at any given time as well as overall information about your house.