Duplicate the layer you want to mkae the pattern from. One way you could duplicate the layer is by going to Layer/Duplicate Layer from the Photoshop screen.
Step2
Select the Rectangular Marquis Tool (RM). The RM tool looks like a rectangle made out of dotted lines. It shares space with the Circular Marquis Tool.
Step3
Draw a rectangle with the Rectangular Marquis Tool around the area that you would like to make a pattern.
Step4
Go to Edit/Define Pattern from the top of the Photoshop Screen.
Step5
Type in a name for your pattern. Hit OK, then Ctrl-D to deselect.
Step6
Select your Paintbucket tool from the vertical toolbar. Now look at the control bar across the top of your screen. The first drop box contains the choices of "Foreground" and "Pattern." Choose "Pattern."
Step7
Directly to the right of the box that says pattern, you'll see a pattern swatch. Open up that pulldown, and you'll see your new pattern swatch as the last choice. Select it.
Step8
click the paintbucket onto your image, and see your new pattern in action!
Tips & Warnings
Always keep a spare file of your image before you start making adjustments.
Get in the habit of duplicating your layer before you begin.
Making a new pattern will not automatically generate a new layer 9one of my pet peeves), so make sure you make a new layer. Otherwise, your image will just be your pattern.