In the mapping tool, FormSketch, there is a drawing menu at the bottom, which allows you a number of options for your map drawing.
One of these is called Floor Planner, and it is represented by a small floorplan symbol.
Click on this symbol. and you will be given a new menu, which will give you the options for floor planning, including adding doors and windows.
Adding a door or window is as simple as clicking on either the door or window icons, and then finding the spot along the wall where you would like to add it.
You can adjust the door as necessary, by selecting one of the flip options (Flip H, or Flip V) to switch it around horizontally or vertically. If you click on the Arrow tool in the top menu of the map, you can also select the door or window to move them around or change the size with the markers in the corner of the door/window map icon.
To remove the door or window, select the Delete option from the menu at the top of the page and then click on the door, or use the eraser tool to delete a part of it.
