To access the buying/adding area, click on the button Buy buildings and land button on your land plot on your homepage.
1)Click on the picture of the item you would like to add. You have a choice of roads, buildings, a pond, garden and miscellaneous items that produce goods.
2)Click the location on the land that you would like to add that item.
3)Click the Buy button. (You can do this after each item or you can repeat the process for several items and then click buy to add them all.)

Note: If you change your mind click Refresh page button before you click buy to clear what you have placed there. Items and buildings are not moveable so make sure you are sure you want to buy as once they are purchased if you change your mind it will require you to demolish which will cost you more coins.