All you have to do is click on the bottom of screen where it show the price with the house
or the price with the house and the furniture. Click on it then it will purchase it or,
ask you if that house is what you want.

you go to the bottom of the screen and click on the thing you need to click on. which
house do you want to buy? it'll say. the one already built and furnished or buy the empty
lot and choose which house you want. Then you can choose which house to buy. remember
don't make it too expensive. or you won't have enough money for food and buying furniture.
(you must be a newbie??)