Start a new image that is 1 inch square with a white background. Duplicate the layer by clicking on Layer, Duplicate Layer.
Scribble or draw anything you want onto this square and apply different filters until you have a "pattern" that you want to use to fill an area. When ready, save it using Edit, Define Pattern. When you have 4 or 5 such patterns created and saved using Edit, Define Pattern, you will open a new image with a white background and the new image should be roughly four to six inches in height and width, but not necessarily square. The new image may be 6 x 4 inches or 4 x 6 or 5 x 5 or 5 x 4, etc. Duplicate the Layer using Layer, Duplicate Layer. Use the tools in the toolbar to select various small areas inside your new image. When you have one area selected with a dotted line around the area, use Edit, Fill,
Pattern Fill and select one of the patterns you made to fill the selected area. Repeat this process to create any type of composition you desire. Use layers for each new selected area so that you can move and reposition your pattern fills. Delete the layers you do not like.
Save and move the fills you like. Before flattening the layers, play with the opacity control in the layers window, using the down arrow by Opacity, and the slider bar. When the image is the way you want it, flatten the layers
by clicking on Layers, Flatten.
Hint: If for some reason you cannot "fill" a shape in a new layer, first click on Layer, then click on Rasterize Layer and re-try the pattern fill, using Edit, Fill, Pattern and clicking on the pattern you want to use. In the Fill dialog box you may need to click the down arrow in order to see the word Pattern. You must click on Pattern to reach the pattern dialog box where the selections can be seen.
The image above was created by a student new to art and new to PhotoShop, just by using the polygon selection tool to define areas to fill, and using patterns that she created with pens, brushes and filters.