STEP 1: Find the non-market app.
This is a broad step, and often you will have discovered the app by accident. If you’re looking, search engines like Google and websites like Droid-Life are a great place to start. Perhaps the best way to find non-Market apps is to be active in an Android community. Android fans love to post about that new cool app they’ve found. There are also websites like Slide Android Market and AndAppStore, which cater to non-market apps and users who do not have access to the Android Market.
STEP 2: Verify that the app is in the right format.
The file you will download has the extension APK. APK stands for Android Package, and it indicates an Android app installer. Other file types will be sources and resources for developers.
STEP 3: Download the APK file to your phone.
Generally, you will download it to the browser’s default download folder. However, location is irrelevant, so place it wherever you find most convenient.
STEP 4: Configure your Android for a non-Market installation.
Press Menu, then Settings, and then Applications. Check the box labeled Unknown Sources.
STEP 5: Download and install an Android file manager.
Note that you can use the Android SDK to install APK files. However, most users will prefer the convenience of a free file manager app. The most common is the free Apps Installer from the Android Market, but there also many great free and paid third-party options.
STEP 6: Install the new app.
Start the file manager, and select the install option. Browse to the downloaded APK file, and then select it. Select OK, and follow the on-screen instructions, if there are any. This is usually a hands-free process.
STEP 8: (Optional) Secure Android.
Press Menu, then Settings, and then Applications. Uncheck the box labeled Unknown Sources.
For those who prefer to use the Android SDK, replace steps #5 and #6 above with the following:
STEP 1: Download and install the Google Android SDK on your PC.
STEP 2: Type adb into the command shell to access the SDK tool (adb.exe).
STEP 3: Install the Android USB drivers.
The Android USB drivers specifically, not general Windows drivers, are necessary for using the SDK.
STEP 4: Connect the phone to the computer via USB.
STEP 5: Disable USB storage.
Press Settings, the SD card & phone storage, and then disable Use for USB storage.
STEP 6: Install the app.
Type adb install full_filepath_and_filename
STEP 7: Enable USB storage.
Press Settings, the SD card & phone storage, and then enable Use for USB storage.