Peel the backing paper off both sides of all the laser-cut parts (11 in the 4x4 kit, 15 in the 8x8 kit). It’s easiest to start at a corner, catching the edge of the paper with a fingernail.
The laser-cutting process can leave some paper soot at the edges. If you like, wash these parts off with soap and water, just be absolutely certain that all the parts are completely dry before assembling!
Use only soap and water when cleaning these parts. Some chemicals, including rubbing alcohol and alcohol wipes, will damage the plastic!
If using the STEMMA cable, cut it in half along its length, strip and tin the ends of the wires.
For a tethered device, you only need the half with the plug.
For a wireless device, save the other half. Clip off the header pins, strip and tin both ends of these wires.
You can still build the kit if you don’t have the STEMMA cable but have other wire around…you’ll be soldering directly to the pads on the edges of the Trellis board in that case, it’s not quite as plug-in simple.