Android Question I Need call to the left button of the device mobile

Greetings.

I need call the left button in this button sometimes the people put options for help to the peolple.

This button is inside device mobile .The button is made by Samsung.

example:

You have a right button for back to other screen,the center button for exit of the app,and the left button for options


please,What is the name of this button(name of the object)?

I can't renember.