Just say "Alexa, open OneBusAway" to get started. You'll set your city and favorite stop, using the stop number. Then, just say "Alexa, open OneBusAway" to get arrival times for your favorite stop. You can also change your city or stop at any point, or ask OneBusAway to repeat the last information.
You can find your stop number on the placard in the bus zone, in your OneBusAway mobile app, or on your agency website. For more information on finding your stop number, see http://bit.ly/stopnumber.