Is this sign used for buttons on clothing?
No, this sign specifically refers to a push-button, like those found on an elevator, remote control, or machine. For clothing buttons, you would use an 'F' handshape and tap it down your chest to show where the buttons are located.
Can I use my index finger to press the button instead?
While it might be understood in context, it is best to use your thumb with an 'A' handshape. This is the standard and most widely recognized way to sign 'button' in ASL.
Do I press the button once or multiple times?
A single, distinct press is usually sufficient when referring to the noun 'button.' If you are describing the action of repeatedly pressing a button, you can tap your thumb multiple times to show that continuous action.