Noise is really a wonderful tool to make easy texture effects. What does this tool do? It changes some pixels in an image, adding darker and lighter pixels to give a granular effect. Let's try. Draw a simple form to test the tool (I'm using an ellipse):

Click inside with your Magic Wand. All the inner pixels will be selected:

Go to Adjust/Add/Remove Noise/Add Noise:

You'll get this dialog window. Let's see the meaning of each item:

Random — creates a granular effect that adds texture (randomly...)

Uniform — changes the color of the noise to resemble the original pixels

Gaussian — makes most of the noise resemble the original pixels more than the Uniform option

You can use black-and-white noise pixels by marking the Monochrome check box. Set a value for the noise. Here I'm using Uniform, 4, and applied it twice:

Try the settings, play with them, and have fun!