The video is pretty good but there is one error. You don't need to set the gear to 4, just to the slackest setting (gear 1)
The nut (that is fixed to the cable) slots into the cassette arm. You relieve tension on the arm (using a small allen key), grab the nut with pliers. Note that the nut has some flat sides which you have to align with the slot int he cassette arm, you need to apply a very small rotation to line up the flats then the bolt and cable come off.
Do NOT remove or adjust the nut and bolt on the cable, this is set precisely.
There is no need to adjust cable tension on re-fitting. If you do need to adjust the tension, this is where you need the gears set to 4 so you can align the yellow marks using the barrel adjuster.

Make a note of the colour of the anti-rotation washers on each side, they set the hub axle at the correct angle for your frame. You shouldn't need to remove the wheels nuts completely but if you do, you need to refit the correct colour of washer.

Tools:
-wheel nut wrench. I prefer a small box wrench that encloses the bolt, rather than an open crescent wrench. Vertical dropouts don't need as much tightening so can use a shorter wrench. Horizontal slots need more wellie so a longer wrench.
-Pliers. Small, needle-nosed such as on Leatherman tools. Electricians pliers are small and light.
-Tiny allen key or small nail to fit onto hole in cassette arm. You can work the cassette arm by hand but it gets dirty.