Sorry, I could be more informative.
Select the Get Tab activity. Press F9, this will add a red dot on the activity symbolising an breakpoint.
Now press F5 or the run button to run the workflow, once it gets to the breakpoint it will stop, and in the property dialog you will now see all activity variables and the values they have. You tab variable should be null ( i don’t know what you called it so lets assume you called it currenttab )
press F10 to run 1 activity and break.
Now you tab variable currenttab should have an instance of a chrome tab, and you can see all properties on this object, one of them should be .url
This is the one you want, so now you know you should reference currenttab.url
You could also just have added a writeline activity
Then type currenttab. the . will trigger intellisense and you get a list of properties on the object, one of them should be url, so would make sense to use that.