Doing something when link/passage is clicked?

Hey, i am currently trying to blend in with sugarcube. Already got some stuff out of the documentary.

But what i coudn´t find because i cannot put it into the right words:

How to do something (e.g. changing variables) when something is clicked?

The Intention Looks like this:

Passage "Stayhere"

<<set $text to "Hello">>
<<print $text>>

[<<set $text to "Okay let´s talk">>Stayhere| Let´s have a talk]]

same question:
How to do something (e.g. change variables) when someone clicks on an internetlink.