The prime field Fₚ can be represented in the complex numbers as the set of roots of the polynomial xᵖ - x.
Now, to build a finite field of size pⁿ, you find an irreducible polynomial P(x) over that prime field and put a field structure on the roots, seen as an n-dimensional vector space over Fₚ.
So all you have to do to map the finite field of size pⁿ to the complex numbers is to find a "good" Fₚ-irreducible P(x) and plot its complex roots. Then you associate points on the curve with such pairs of complex numbers and map them on to the torus as you do with all the rest, marking them as "hey, those are the Fₚ(n)-points of the curve".
In principle, any polynomial P(x) will do; in practice, I suspect some polynomials will serve much better to illustrate the points on the curve than others. We must wait for the follow up paper to see what kind of choices they have made and why.
Now, to build a finite field of size pⁿ, you find an irreducible polynomial P(x) over that prime field and put a field structure on the roots, seen as an n-dimensional vector space over Fₚ.
So all you have to do to map the finite field of size pⁿ to the complex numbers is to find a "good" Fₚ-irreducible P(x) and plot its complex roots. Then you associate points on the curve with such pairs of complex numbers and map them on to the torus as you do with all the rest, marking them as "hey, those are the Fₚ(n)-points of the curve".
In principle, any polynomial P(x) will do; in practice, I suspect some polynomials will serve much better to illustrate the points on the curve than others. We must wait for the follow up paper to see what kind of choices they have made and why.