Place one piece of 'A' vertically with one piece of 'B' and 'C' horozontally at its base.

Using the Electric Drill, drill two holes into A at its base so that they go through A and into B.

Drill two more holes on the other side of A and into C.

Using the Screwdriver, screw all three pieces together through the holes that were just created.

All three pieces should now be joined.

Repeat the same process to create the other corner of the base. Screw the two corners that were just built together using the same process.