It all starts with a rectangle. It's amazing--a rectangle can be a door or a window (or about a thousand other things). Your perceptions of the art you see depends on your frame of mind as much as the art itself. To draw these subjects, start with a rectangle and follow your instincts. Most people have seen enough doors and windows in their lifetime that drawings of these subjects will be almost instantly recognizable.
Draw a rectangle, approximately two times as tall as it is wide. This is the outline of the door.
Draw a square or a pair of rectangles, spaced apart, centered in the lower half of the door. Draw a square centered in the top half of the door. These are the designs in the door.
Draw a circle on the right side inside of the rectangle, half way between the top half and the bottom half of the rectangle. This is the door knob.
Draw a rectangle. This rectangle should be slightly taller than it is wide.
Draw a rectangle around the first rectangle, so the first rectangle is centered inside the rectangle you are drawing now. There should not be much space between the two rectangles. These two rectangles form the outside of the window.
Divide the inside rectangle in half with a horizontal line. Draw a second line just above the first line, so there is little space between the two. These lines form the boundary between the bottom pane and the top pane.
Draw three diagonal lines, parallel to one another, through the bottom pane of the window. These lines represent the glare. Draw three diagonal lines, parallel to one another, through the top pane of the window.
For a more realistic drawing of these subjects, look at pictures of actual doors and windows for inspiration and realistic details.
If you wish to draw the door in perspective, you'll need to establish the vanishing points. The vanishing points are the places on the horizon where three dimensional objects would disappear, if they were to continue into the distance. Once the vanishing points have been established, all vertical lines of the doors and windows are angled toward the vanishing points.