Creating an abstract website navigation header
Start by creating a new file of header size. Apply a solid color to the background.
Select brush tool. Right click the and select "Chalk 23 Pixels" brush from the custom brush palette.
Create a new layer and apply randomly.

Similarly select different brush with different color and apply randomly.
Change the layer mode to "Vivid Light".
Select and merge both the layers. Now select "Dune Grass" brush with the diameter settings as shown.
Select white color and apply this brush as shown.

Create a selection as shown using polygon lasso tool. Press Ctrl+J to copy paste the selection in a new layer.

Double click the layer to open layer style window. Apply settings as shown.
Repeat the above steps for the other side.
Create a circle using elliptical shape tool.
Double click the layer to open layer style window. Apply settings as shown.

Similarly create more circle shapes with different sizes and different layer modes. Place them as shown in the image below.
Populate the header by inserting company logo and navigation links.