How to make my Nikon DX lens autofocus?

How to make my Nikon DX lens autofocus? - 1

Added (1). So I bought a new Nikon lens for my camera and the guy in the shop said it autofocuses but it doesn't.

Added (2). Lens is: AF-S NIKKOR 35mm 1:1.8G

What camera?

Switch on the motor.

If the motor is switched on, talk to him again.

AF-S lenses have built-in motors, so they even autofocus on the D3xxx and D5xxx.

You didn't mention the camera body model number.
Be sure the switch on the side of the lens is set to MA.
If you have a body with a motor drive (D90, D7k series, …), be sure the switch on the body near the base of the lens is set to AF.

Just push the button towards AF on lens

If it's broken, bring it to the service center.

If it's a motorless lens on a motorless body then no way.