Document Actions using Route

Hi

I want to learn how to use the “Actions” feature under “Customize”. Yes, I can use
a script to add a button but hwo can I use Actions to do this. I tried

Actions:
label : Related Projects
Route
route = /app/project/{{ doc.project }}

But I cannot figure out how to define the route-definition.
I tried

/app/project/{{ doc.project }}
/app/project/{{ project }}
/app/project/doc.project
/app/project/project
/app/project/
/app/project/<doc.project>

But none is working . Can someone help ?