Although the 3D Plan Editor can generate many kinds of windows and doors, you may still not be able to create just the door or window you need in a given situation. If this happens, try just creating the door or window opening with the editor, then treat the glazing/door as furniture to be added in the Design Editor.
The selection of windows and doors above is available in the Furniture Album/ Party Gallery, but you can also create your own.
When you load such items, the first step will be to rotate them to the proper orientation. Use this little chart to help:
Now position the door or window tight against the correct wall with a Push, then switch to a front or side view of the room and set the final dimensions, so the item fills the hole in the wall.
Curtains are handled in much the same way. The illustration below will give you some idea of the effects you can achieve using this technique.