This Tutorial works with any of the following: Squares, Grids, Lines or Dots.

Firstly open a new blank or another project you would like to use this effect on.

Start by adding a background preferably something which your grid, squares, lines or dots will show up on.
For this I choose a black background and white diagonal lines.

When we have done create a new layer (Layer> New> Layer...) A transparent one.
Now we are going to use either Rectangular Marquee Tool, or Elliptical Marquee Tool depending on your choice, I choose to use Rectangular Marquee Tool (We can also select any of the Lasso tools).
Once we have done this on the menu at the top we should have an option called 'Feather'.
Set the feather to about 10 px, the higher or lower we go depends will change how much the filled area will break up.
Now use the selected tool to make a selection on your document.

We can now fill this area by using the Paint Bucket Tool with our selected pattern.
WE NEED TO MAKE SURE that the 'Mode' is set to Dissolve.

Use Control D to deselect the area now and with this layer adjust the opacity because I find the lines are too solid at the moment.
I'm going to set my Opacity to about 35%.

WE'RE FINISHED!

An example for the use of this tutorial: