Step 3: Attach the Arduino to the Chassis
Once you have the standoffs firmly attached to your Arduino, line up the bottom one with the bottom of the backmost mounting strip (um... just look at the picture). Attach that into place, then line up the front standoff with the next mounting strip, and screw that in place. Yippee, you're done!
Note: There's a zip-tie in the picture because I did step 4 before this one... then realized that it's easier to do this step first.