Firebase increment function?

Question
1

Hi does anyone know how to use the increment function of firebase?
In order to understand what i mean i leave the link bellow.

2

I also found this info, do you know if its possible to use it in appgyver?

https://firebase.google.com/docs/firestore/manage-data/add-data#increment_a_numeric_value

3

do you know how this work?