The unit cell of sodium chloride is a face-centered cube with
a = b = c = 5.45Å and with lattice points at the corners of the unit cell and in the center of each of the faces. (In the drawing here, the purple Na⁺ ions are taken to be the lattice points, but it would also be correct to identify the lattice points as Cl^- ions or, in fact, to be the mid-points between Na⁺ ions and Cl^- ions.)
By translating this unit cell by one cell length, the contents of the unit cell are repeated in that direction. (click “Translate a” and “Translate b”).

This representation of atoms as “little balls” is not accurate - the Na and Cl atoms would be more correctly represented with their ionic radii so that the oppositely charged ions are “just touching”. (click “Ionic Radii”).

In this case, each positive Na ion is contacting six negative Cl's; and each negative Cl is contacting six positive Na's. (click “Na Coordination” and “Cl Coordination”).