So, now that your Pi is off and unplugged, let's connect the matrix hat to the pi and the LED board to the matrix hat. If your Pi isn't already in it's case, now's a good time to put it in there.

Install the matrix hat by lining it up with the GPIO pins on the Pi and pushing it gently down with even force on both sides. Make sure that the pins are lined up correctly, so that the female headers on the hat exactly cover the GPIO pins on the pi. If you misalign it, it's not a catastrophe; just gently pull it back off and straighten out any pins that got bent.

Once you've got the hat on, put the Pi to the right of the assembled LED board (double check the power connections again, and make sure the arrows are pointing from the Pi down the length of the board) and connect up the IDC cable to the matrix hat.

Next, you'll want to connect the spade terminals for the power into the matrix hat's terminal block. You've got two spade connectors per side, but they should both fit in there fine. Loosen up the screws first and - This should go without saying - make sure you put the 5V terminals in the side labeled + (these should be red, but - again - double check your connectors and don't assume they got manufactured correctly) and the GND terminals (these should be black) in the side labeled -. Once they're in there, tighten the screws on top of the terminal block, and you should have something that looks like the header image for this step.

Now - you may have noticed that this particular configuration leaves one-half of the spade terminal on either side exposed, hovering mere milimeters above the matrix hat (and not very much further from each other.) AND - the spade terminals will very soon be carrying both several volts and several amps of Raw Power. Is this, (I can hear you asking from the other side of the screen) really The Right Way To Do It? Is it, (you lean in closer and whisper), A Good Idea?

And the answer is (I respond, shrugging my shoulders) - no, it is not. The right way to do it would be to strip the spade terminals off the power cables and re-crimp them into the correct connector for that terminal block (or to leave them as bare wires and connect them without a connector into the block). Failing that, you could put some heat shrink tubing around the exposed side of the spade connector or just wrap it in electrical tape. But the world is fallen and man is lazy and vain, so I haven't done that.

But - wrapped or unwrapped - the spade terminals are connected to the terminal block, and we're ready to move on to the next step.