Most of them install lots of apps in your android phone, sometimes another person may take you phone and access your personal apps. Applock is an android app that will help you to lock your apps and protect from unauthorised uses. You can use password protection or pattern.
You can simply install this app on your mobile after the installation you can lock incoming calls, install/uninstall and settings. You can easily hide Applock on your mobile and it start from dial pad.