In this photoshop tutorial, learn how to create and use patterns, but only on basic examples.
Step 1CTRL +N (New windows) with 2px wide and 2px high canvas:
Step 2Zoom in and click once in the upper left corner of your canvas with pencil tool using this settings like on picture below:

Step 3Now is time to Save our pattern.
Go to Edit > Define Pattern, type your pattern name and click ok.
Step 4Now we gonna use our pattern.
Create new canvas of any size with white background.
Create new layer and draw square using Rectangular Marquee tool.

Click Ctrl + Delete to fill your square.
Chose pattern and select your pattern.

And the final result is: