You've found that hot new app on the Android Market, and you can't wait to click the Install button. But you're getting the message that the app isn't compatible with your device. Being the good Maximum user that you are, you'd rather find out for yourself. Those messages are sometimes wrong, after all. Or perhaps you want to take advantage of the daily giveaways in the Amazon Appstore. Or, if you're one of the millions of Kindle Fire owners, you may want more choices than the limited Amazon Appstore provides. All of the above comprise sufficient reason to start sideloading apps to your Android device.
Step 1: Get Some Apps to Sideload
The reason you sideload apps in the first place is because you're sourcing them from a place other than the sanctioned method, which is usually the Android Market or some device-specific boutique app store. Android Apps come in the form of .apk files. You can procure such files from a prior device backup, straight from a developer's website, and of course from… the Internet (you know the deal).
Next, transfer those .apk files from your PC to your Android however you like: on a microSD card (image above), through a cloud service such as Dropbox, via a USB transfer, etc. Just remember what directory those files end up in, so you don't have to root through too many folders looking for them later.
Step 2: Tweak Applications Settings
The default setting in Android is to not allow the installation of non-Market applications. Fie on that! Go to your Android device's Settings, and under Applications, check the "Unknown sources" box (image below), allowing you, in effect, to sideload. Some unfortunate souls may have tyrannical devices that have modded the Android OS to not allow sideloading at all, in which case they'll have to look into rooting the device or installing custom Android ROMs. But that's a whole other How To.
Step 3: Install the Apps Through a File Manager
To install your .apk apps, you essentially launch the files through a file manager app. Many Android devices come with a file manager preloaded. For the rest, there are tons of file managers out there and a good handful of high-quality free ones. If you have access to the Android Market, like most Android users, we like Metago's Astro File Manager or Rhythm Software's File Manager HD for Honeycomb tablets. For folks locked into the Amazon Appstore (users of the Grid10, Kindle Fire, etc.), we prefer ES File Explorer.
Because you heeded our warning to remember what folder your .apk’s are in, you just need to launch your file manager and find them (image above). If they're on a microSD card, you'll probably need to hit the file manager's Up button a couple of times to find the "Removable" directory. Touching an .apk icon will open the Package Installer, where you can touch the Install button to finish the deed (image below). Now that app, whether it will function properly or not, is ready to launch. Enjoy the sweet freedom of the gray market!