The user interface for moving and resizing windows under Ubuntu is essentially the same as that found on Windows. You can click and drag the titlebar of any window to move it, and you can click and drag the "handles" of any window to resize it.
Ubuntu goes one step further, however. If you hold down the "Alt" key on the keyboard, then clicking and dragging anywhere inside a window will allow you to move it. And clicking and dragging using the middle mouse button (pressing in the scroll wheel for most mice with scroll wheels) will allow you to resize. Using these quick shortcuts can make window management much easier as they don't require you to target very small areas on the screen to begin your mouse drag.