You need the following to assemble: metal saw (if you need to cut the wire shelf).
Before you start: Finish assembling the drawer system units with frame sides, crossbars and baskets. If needed, cut the wire shelf to the desired width.
Click on the respective clips onto the outer frame sides, by snapping them onto the runners. The U-shaped part of the clip is where the wire shelf mounts, and should be pointing upwards. Aim for one position close to front and one close to the back of the runners.
Then click the wire shelf into place (use the second wire from the edge) in the U-shaped part of the clip.