Question of 'Explaining SNARKs Part I'

I new in ZCASH, and read the blog
It say:

when p is large, given an element h in Z∗p it is difficult to find the integer a in 0,…,p−2 such that ga=h(modp).
Why? g0=1,g1=2,so a=h-1.
As ”exponents add up when elements are multiplied”, we have for a,b in 0,…,p−2 ga⋅gb=ga+b(modp−1).
I don’t understand this.

a is not h-1. Perhaps you think we’re talking about the additive and not multiplicative group and that’s confusing you.