Why do apps downloaded from online not work on LG escape 3?

[AC Question]

Everytime I download my apk files from websites online and try to open it them on my LG escape 3, it says "Unfortunately (app name) has stopped working. Ive tried clearing the data on these apps and they still dont work. What do I do?

 

[chanchan05]

Stop downloading apk from random sources and get them from Google Play.