The Android™ operating system offers its users the unique option of installing applications which are not part of the Google Play™ store. You can simply copy any APK file into your mobile phone and launch the installation just like you can on a computer. This should be done at your own risk, of course, but you can find applications that are not part of the Google Play™ store.
Almost all Android-based devices disable this feature by default as a way to prevent potential Android™ software damage to the handset. It can, however, be enabled quite simply. Adventurous Android™ users can follow the instructions below to learn how to do it.
Enabling installation of third party apps on any AndroidDevice :