Only played oblivion and skyrim. And I don't quite understand how these roles play. Let me explain, the emperor is like the president of the whole land. The high king is like the governor and there's multiple high kings, one for skyrim, one for cyrodil ect. But there is only one emperor. Am I correct with this?

The High King refers to the "King" of Skyrim, which is a province of the Imperial Empire.

Emperor, is the 'head' of the Imperial Empire.

There are counts, and Jarls, which could be viewed as governors for Cyrodriil and Skyrim, respectively. They are under the High King, and Emperor.

In response to your spoiler, yes.

Correct, although I assume the title would be different in let's say High Rock.

For a second I thought this would be about who you'd want to be. Thank the Gods.

High King is still the title in High Rock. I think it is in Hammerfell as well, though I'm not sure.