That’s probably because the .apk is not properly signed or you’re using a
minSdkVersion bigger than your current phone’s android version.
For the first case use this to sign your .APK’s if you have trouble signing them.
For the latter, check your current Android version and the SDK version you installed and go here to ensure the SDK version you installed is not bigger than your current Android version. In case it is, you need to install a lower SDK version and compile your project using the lower SDK.
I’m not expert in Android but from the few stuff I know, I believe it’s a good practice to set the
minSdkVersion to a somewhat lower Android version (like 4.4), and
targetSdkVersion to a bigger version (like 6, 7, or 8 already).