To assemble the corten steel planter, you only need the supplied bolts, nuts, and spanner.
The planter is made up of 5 different pieces. Find the bottom, the other 4 pieces are the sides. The side panels have 1 side that is the top, recognisable by the square part.
Secure one side panel to the bottom with two bolts and nuts, using the spanner. Double check that you have got the right side up.
Secure the remaining three side panels as described in step 2. Also secure the side panels to each other.