TinyWM is a tiny window manager that I created as an exercise in minimalism. It is also maybe helpful in learning some of the very basics of creating a window manager. It is only around 50 lines of C. There is also a Python version using python-xlib.
It lets you do four basic things:
1. Move windows interactively with Alt+Button1 drag (left mouse button)
2. Resize windows interactively with Alt+Button3 drag (right mouse button)
3. Raise windows with Alt+F1 (not high on usability I know, but I needed a keybinding in there somewhere)
4. Focus windows with the mouse pointer (X does this on its own)