Start by peeling the paper backing off of the plastic plate. Begin at a corner, it should come off easily.

There are little holes and cutouts, you may need to poke them out using a screwdriver or pen

There are outlines showing how the Arduino and breadboard go on, make sure the print is right way up or it'll be confusing!

There are four mounting holes for various Arduinos. Unfortunately, each Arduino revision has slightly different 'preferred' mounting holes. Here we show what we consider the preferred holes for the Uno R3 which is likely what you have. Place the screws into the plate from the bottom of the plate so they stick up. Screw on two hex nuts to keep them in place

Place the Arduino on top, it should slide onto the bolts

Attach the Arduino securely by screwing on the last two hex nuts
The bolts are made of nylon so they will flex a little if necessary. Use pliers to get a grip on the hex nut near the DC power jack

Remove the paper backing from the half size breadboard and stick it on next to the Arduino.

Watch that the bumpy side is not next to the Arduino so it it will flat against it.

Finally, place four bumpers on the bottom!