What thing in camera reduce noise?

Usually i take pictures with my iphone 4s but the image it captures its so noisy so i decided to buy dslr camera so i want to know what thing reduce image noise and makes the image clean… What thing makes my 4s capture images so noisy? Is it for the low 8mp it has

The ISO is what controls 'noise' in a DSLR - ideally you keep it as low as possible (except when you absolutely have to raise it to get the shot).

The reason iphones (or any cameraphone) is poor quality & noisy (especially in low light) is down to the fact that manufacturers cram too many pixels onto tiny sensors - this makes noise worse. DSLR's have huge sensors compared to a phone & this makes a real difference.

I suggest that having splashed out for a DSLR, you actually take the time to learn about the basics of photography - take a class or use online resources to learn about exposure, lighting & composition. Then you will get the most out of your fine new camera.