Every way your subwoofers can be wired, the impedance each one presents to the amplifier, and the speaker cable it needs.
Check what your amplifier can run down to. Lower impedance gives more power, but also more current and more heat inside the amplifier. Go below what it was built for and it drops into protection at best — and burns out at worst. The figure is in the datasheet, usually as “1 Ω stable” or “2 Ω min”.
The colours in the diagram. Red is the positive side, black the negative, orange is the jumper between the two coils on a DVC subwoofer, and grey is the wire between two subwoofers in series. The steps under each drawing say what connects where. A green box around the impedance means the combination lands on one of the values amplifiers are normally built for: 0.5, 1, 2 or 4 Ω.
Lower impedance is not automatically better. It buys more watts, but the amplifier works harder for each of them and the damping factor falls — the bass gets looser. Where two combinations give the same impedance both are shown, and electrically it makes no difference which you pick.
About the cable suggestion. It is worked out from the current at the impedance shown: I = √(total RMS / ohms). “Min.” is what many people run, “best” is one step thicker. Using CCA instead of OFC, go two steps up. This is the speaker cable — the power cable from the battery is a different matter, and the cable and fuse tool works that one out.