How is adding these schemes meant?

Question

Could someone be able explain how to add prime divisors or their multiplication with the locally finite set $n_{Z} Z$ in $\sum n_{Z} Z$? https://stacks.math.columbia.edu/tag/0BE0#:~:text=A%20Weil%20divisor%20is%20a%20formal%20sum%20D,the%20Weil%20divisor%20associated%20to%20a%20rational%20function.

Answer 1

A Weil divisor is a formal sum, i.e. an element of the free abelian group on the prime divisors.