You can build a multi-city or open jaw itinerary using the general search page or Trip Builder.
When you click “Multi-City” many segments open up. You can add as many destinations as you’d like and click “Search for Fares.”
Keep in mind that many of our discount consolidator fares don’t allow complex itineraries like these–you may get ruled out for a discounted fare. Sometimes it’s cheaper to break up the ticketing, where you price each segment separately.