Remove the Feet
The first step in assembly is removing the feet from the body. They are secured using the two 6#32 thumbscrews at the top of each foot. There is no need to fully remove the screws, simply loosen them and the feet should drop away from the body. Depending on the motherboard and expansion card you plan to install, you can remove the appropriate number of standoffs from the feet in preparation for them.
Attach the feet
To install the feet, fully remove the 6#32 screws from the top of the feet, position them to align with the correct holes at either side of the body, then use those same screws to attach them to the body.