Interface of application is simple, easy using, beside does not require any additional settings.
The first, press “Enable back button” button then touching and sliding to find “BackHomeButton” line that is under service tag(Settings--->Accessibility---- > BackHomeButton). Click on line which has found above then switching it on to present “back” button .Touch and slide on “back” button to move it to suitable position .

Beside, you can also change size of back button or reverse them by pressing on button at top bar of app screen.

If you use android 5.1.1 or higer , the third button is soft power button, default is quick setting button.

*This app uses Accessibility services.
Accessibility services is to use functions of “Back button”,”Home button” ,”Quick settings button” for less than android 5.1.1 and “Power button” for android 5.1.1 or higher