Adding value to a variable created

It is a simple question and I hope I get clear.
I want after an “If” statement, as a result to add or abstract a number from a variable. By “variable” I mean not a parameter, but just a simple named variable that has a number (which I don’t know how to create on dynamo, I have handled only parameters and categories until now). This number I want to be increasing or decreasing after some conditions I set.
Thank you in advance!

Hi @Eles
Welcome to our Dynamo community.
It is difficult to understand what you are trying to convey!
Can you please provide a visual representation of what you need?