First Step: Create a 3x3 Image
Second Step: Zoom in 3200%
Third Step: Grab Pencil Tool Size 1
Fourth Step: Dot the pencil ONCE in the center of the square.
Fifth Step: Press Image, Define Pattern
Step Six: When you want to put in the dots, press Edit, Fill, Pattern, press the little arrow, and press on the dot pattern you created.
Step Seven: There are no more steps!