So here you've got a cylinder with three concentric ellipses on each side. The reason for this is... well, my wheels weren't big enough to start with, and in my second attempt they still weren't big enough. Yeah, there's no magic here. The inner-most ellipse is the result of what we were doing in the previous step - I laid in the ellipse so that it fit snugly between the first vertical and the two horizontals, and I used a degree that made it so the contact points above and below (where the ellipse touches those top and bottom horizontal lines) align vertically. As explained in the videos, this only matches up when the ellipse accurately represents a perfect circle within the context of this perspective system. Once this has been achieved, we can draw the remaining vertical to close off the ellipse in a plane - which also happens to now represent a perfect square in 3D space.
Note: Freehanding ellipses with all of this business of specific degrees and matching up contact points is hard. You're not likely to get it down perfectly, so as I mentioned above, you are free to use ellipse guides, rulers, etc. to make your life easier. If you happen to do it freehand, that's fine as well, just don't get frustrated if you don't nail your ellipses. A bit of deviation won't ruin things, it's totally fine.
Another thing worth mentioning here is that unless your wheels are at an angle relative to the body of the vehicle, you should start the wheels on the same axle off as a single cylinder. You can cut them up later, but in general it's a lot easier to work through these phases with larger cylinders rather than squatter ones already cut to the size of each individual wheel.