Hey guys, i'm new to javascript I hope you can help me out

Hey guys, i'm new to javascript I hope you can help me out

I looked up to google on this one but no luck I hope you can help me out,
I got no codes to present here or something I just would like to ask what
is the use of Calc.Input.value function in JavaScript? I'm kinda confused
of what's the use of that one. Thank you in advance guys! Much love :))