Start by installing the M3 standoffs to the four mounting holes. Finger tightened them so as not to strip the holes. If you find the mounting holes are too tight, I suggest tapping using an M3 tapping tool to create threads.
Install Hex Nuts
Place the M3 hex nuts onto the male threads of the standoffs. Finger tighten at first and optionally use a pair of pliers to firmly tighten. Repeat for all four standoffs.
Grab four M3 x 5mm mertric screws and begin to fasten into the mounting holes on the Pi Zero board. The mounting holes might be tight so I suggest using an M3 screw tap to loosen up the holes and create proper threads.
Pi Zero Placement
Grab the Pi Zero PCB and place it on top of the standoffs. The USB and HDMI connectors should be oriented down towards the center hole in the stand.
Fasten the four screws until fully tightened – Be careful not to over tighten as you could damage the PCB or strip the threading.