X-Plane 9 is a highly detailed flight simulator with a built-in fluid dynamics model to ensure the fidelity of the experience. What it doesn't have, however, is the ability to "pushback" --- to move slowly back from a gate or parking location. To enable pushback in X-Plane 9, you'll need to make use of a third-party plugin created by users of X-Plane 9 to address this shortcoming.
Open your web browser, and navigate to Peter's X-Plane plugin page (see Resources). Click "SimplePushback" and then "Download" to retrieve the SimplePushback .zip file. When prompted, save this to your computer's desktop with the name "simplepushback.zip."
Start Windows Explorer, and navigate to your desktop. Right-click on "simplepushback.zip," and then click "Open with" and choose "Windows Explorer." Double-click the only folder listed, and then click "Windows" to expand that subdirectory; you'll see a file called "SimplePushback.xpl."
Launch a new Windows Explorer window, and navigate to your X-Plane 9 directory. Within that directory, open the "Resources" folder, and then open the "Plugins" folder included within. Drag the "SimplePushback.xpl" file from the "simplepushback.zip" archive to X-Plane's "Plugins" directory.
Start X-Plane 9 by double-clicking its icon in the root X-Plane 9 directory.
Press "Shift" and the "F1" key simultaneously to begin pushback, and then press "B" to disengage your wheel brakes. When you have moved far enough, you can press "Shift" and "F1" again to turn off pushback.