Hi all I want to make app lock in android in which user can lock any application in his phone by using my application

Hi all I want to make app lock in which user can open my app and able to see all applications that are available on his/her phone. Then user has option to select the application that he want to lock. When user select particular application. After all this when user again want to open application that he locked by using my application, a password screen will be opened and user will enter password to use that app. I am not good in English so if some one didn't understand my question, he can download VAULT Application from google play. I need some help how to start this application.