Global functions will be used with $gf()$
The idea is that you could have inputs as well as an output, unlike globals, which only have outputs.
You could define them in their own tab, and when creating/editing them you could add inputs and use them like global variables in a formula.
Exapmle: $gf(add, 2, 5)$ would return 7, and the function will look like this $num1 + num2$
Of course this is a simplified example.