You can use an existing global variable, a context variable defined in your Job, or a Repository-stored context variable applied to your Job in any component properties field.
In the relevant Component view, place your mouse in the field you want to parameterize and press Ctrl+Space to display a full list of all the global variables and those context variables defined in or applied to your Job.
The list grows along with new user-defined variables (context variables).
Double-click the variable of your choice to fill it in the field.