Score and cut the design. (In my pictures, you can see lighter lines - I updated the design file with the better settings, so your paint won't spoil.)

Paint out your design.

I did use much colors, just started with black, then the orange, and added a little extra white line. (I must learn to paint I know :) )

Once your paint completely dried, you can use varnish to secure your design.

Add magnets to the back with a good glue. (you can use glue gun, or some basic glue - in the picture you can see my choice)

I wanted to secure the magnets too, so added one layer of varnish to the back too (even over the magnets). You can skip this step.

BOO! You are finished!