build Android error

Hey guys I made a game in unity for android 4.2 free, however to having a problem installing it. I will explain in detail what I'm doing, to see if you help me. JAVA I have android sdk manager installed everything as requested. 1 - Did the game for android format (in Javascript) 2 - did the build and formed a file (APK) 3 - I put on my memory card 4 - on the phone, click to install 5 - does everything right, speaks to installing this 6 - Appears: application not installed (I have the file of the build to be able to send to my friends in the classroom. But I need build working )

Can you help me?