MMF diagram, of a transformer - why layers are numbered this way?
The numbers represent the MMF, MagnetoMotive Force, at that radius in the windings. You integrate the total current flowing as you move outwards.

$$MMF(r) = \sum_0^r I(r)$$

In your first diagram, as you move through the three layers of the primary, you have one coil with current emerging from the page, then two, then three. The sections are helpfully labelled \$i\$. Once you start counting through the secondary, in the first secondary section current is going into the page, labelled as \$-i\$, which cancels some of the primary current, so the total current drops to two. As you count through the next two sections, all the current is cancelled, and the MMF drops to zero.

The sections have been labelled with the current in that section, and an indication of the MMF at that radius. Unfortunately, labelling the MMF in the middle of the coils is wrong, there is no consistent way to interpret those numbers as the MMF at the left or right side of the coil. It would have been better to label the seven spaces as 0, 1, 2, 3, 2, 1, 0, rather than label the six coils as they have been.