The Porziuncola is the little church St. Francis repaired and made the home of his first brothers; the great basilica was later built over and around it, so you walk into a vast church and find the tiny chapel standing inside it. Because it is in the valley town of Santa Maria degli Angeli, it is a separate visit from the Basilica of St. Francis and the other churches on the hill, and it needs its own place in the day.
To get between the two, take bus line C, which the city calls the Assisi Link. It runs from Santa Maria degli Angeli past the railway station and up to the St. Francis stop and Piazza Matteotti, and back the same way. The Busitalia timetable shows buses about every 15 minutes through the day and every half hour early and late, from about 5:00 a.m. until after 10:30 p.m., with a ride of roughly 15 to 25 minutes (read October 10, 2026). Check Busitalia for the current fare and for the last bus if you are staying late. Taxis can be called through Radio Taxi Assisi at +39 075 813100.
Good to know before you go: if you arrive in Assisi by train, you are already a short walk from the Porziuncola, so it makes sense to visit it first or last, on the way in or out. It is also the easiest of Assisi's great churches for anyone who struggles with hills: the city's accessibility guide describes a level floor throughout, a ramp at the entrance on the right side, and parking with reserved spaces about 150 m from the door.