APK applications are basically Android package applications. If you want to install an app manually from an apk file, this tutorial will show you how to install/execute APK file on Motorola Xoom.
1. Download a file manager app called Astro File Manager and theninstall it.
2. Open Astro and find the app in your memory and select it. It will take you to a screen in the settings to check "Unknown Sources".
3. Do that and go back to the app and you will be able to install .apk file.