Wire the box up first: run all wires that go from stomp-to-pot, stomp-to-jack, pot-to-pot, etc (any wire that doesn’t go to the board). Use the diagram, usually it’s on the same page as the board cut-outs.
Put the box upside down and hold the board just below the box, outside of the box. (when we’re done, we’ll flip the board like a notepad page turning into the box). You can use handy-clips or a piece of 2×4 wood to hold the board in that position.
Start with one piece of hardware (pot, switch, jack, or LED). Estimate the length of wire needed to go from it to the board, and cut that length off (use the single, double, or triple wires depending on if this pot/jack/etc has 1,2, or 3 wires going to it)
Strip the wire(s), 1/8” on the end going to the hardware, 1/4” on the end going to the board.
Solder the wire(s) to the board and hardware.
Repeat for all hardware