Yes, Tri-met is excellent. We have buses and light-rail trains running though Portland.

Max, the light-rail train, will get you from point A to point B for about $2.00. It will get you from the airport to downtown for $3.99. To ride Max, you need to purchase a ticket before getting on. The kiosks take dollar bills (if they're perfect) or credit cards.

Buses are cheaper. Have some change on you; so you don't have to overpay.

The Tri-met Trip Planner can tell you how to get from any place to any other place. You don't need to give it addresses, either. You could ask for a trip from "airport" to "Pioneer Square" (that's downtown), and it will Do The Right Thing. The Trip Planner will also tell you how much the trip will cost.