Each module has four pieces: one bottom, one divider, and two sides; four side labels are optional.  Each module has two cubbies.  The project shown here has two modules, but any number of them can be connected together.

I uses a simple acrylic paint with the grain showing through for a more rustic look.

The pieces are designed for a press fit, so a rubber mallet or dead blow hammer is helpful in achieving a tight fit. 

Fit one end into the bottom with the solid edges facing forward.

Slot the divider into the bottom and the the other end as above.

Fit the back piece last

Using wood glue, glue the modules together.  Touch up the paint.  Glue the labels onto the sides.