How do I put instance variables in an expression?

I am trying to make an RPG game and want to make the attack value differ according to the character stats,which are saved in instance variables. However,I can't find expressions to input the stats of an instance variable into the damage received. How do I do it?I'm quite new to Construct 3,so I hope there's a simple way to solve this.

I think you mean this

Thanks. Really grateful for the help I've been getting.