Nancy,
I have one of these at my office.
If I remember correctly, you grasp the end of the case: the end with the USB and FW plug-ins, and pull it out from the outer plastic shell.
Then, just connect the IDE drive cable, attach the power-cord, and place the 4 plastic glides at each corner of the inside case, and slide the powerboard back into the case.
There should be several screws in the leather case which you use, some to screw the HD to the power board, and some to screw closed the powerboard to the case.
I suspect OWC has online instructions with diagrams /pictures also.
Hope this helps,
Paul