How to do Expressions?

So I'm trying to use the duration expression for the timer and I cannot get it to work. It keeps saying to "use a string and not a number" but I have no idea what it actually means. How do I fix it?

You are editing "On timer" event, parameter Tag should contain a string tag of the Timer. Duration expression returns a number, that's why you are getting this error. Why do you need it here anyway? If you want to compare timer duration, this should be in a separate condition, for example -

System compare two values: Sprite.Timer.Duration("tag")>5