Shut down your Pi and remove power. Plug the Triple Matrix Bonnet on top so all the 2x20 pins go into the GPIO header.

No soldering required.

By default the bonnet has a slim 2x20 header on it. If you need to 'lift' the bonnet above an enclosure, pick up a 2x20 riser header. 

If you want to get access to GPIO while the bonnet is installed, pick up a 2x20 stacking header - the pins will slide through the socket and you can plug something else on top.

The RGB matrix from Adafruit comes with a 2x8 data cable. Connect one end to the matrix INPUT side and the other end to the IDC socket on the HAT/bonnet.

It won't damage the matrix if you accidentally get the cable connected to the output end of the matrix but it won't work so you might as well get it right first time!

If you're using 3 panels placed next to each other, be sure to connect port 2 to the center panel.

Be careful not to put too much pressure onto the bonnet and Pi's GPIO pins while pushing in the matrix cables. Put a finger underneath the bonnet to support it as you press the the matrix cables into their connectors. 

The standard power cables included with Adafruit matrix panels have two 4 pin connectors that can be connected to each of two different panels. To drive 3 panels you need two sets of these cables, and the last connector will be unused. You need to provide 5V DC with at least 8-10+ amps!

Shown here wired with two Female DC Power adapter screw terminal blocks, ready to be connected to two 5V 4A power adapters. You can instead put both sets of power cable forks into one barrel jack and use a 5V 10A adapter.

If using your own wire, be sure it is heavy guage. Do not use breadboard wires, they're too small and will overheat.