T3 Chirp -> understanding Nextjs Routing / Slug

Ive been doing a slight spin of the Chirp project adding some of my own changes, one is you can use clerk with Email too. The problem is Email clerk doesnt have user name, so I want I used firsName for the route name param but also want to move the userId in with route to grab all the user data by Id inside the slug file. I see the ProfilePage getting exported but dont understand how the slug knows to use that page. How do I send state(userId) along with the params that show up on the URL