how can we use javascript in life and for what?

Answer 1

You can do web development. You can even code in javascript for servers with Node.js nowadays.

Or if you are just interested in javascript, you can create userscripts to customize your web for example.

Answer 2

You were using JavaScript when sending this question. I was using JavaScript when sending this answer.

JavaScript is everywhere. Facebook uses JavaScript. Google uses JavaScript.

:)

Answer 3

I m fully agree with @zen.
I will say a little more :
You can create your own webapp as a standalone application. With the help of nw.js or electron for PC.
Or Cordova for mobil app.
You can create what you want and distribute your code how you want...
The only limit is you.
JavaScript can be use to control robot, create game or application, code friendly user script, collect data, showing charts, chat room, make coffee...
No limit, find the idea and code it !!!