Execute the compiled producer binary in order to produce messages to the purchases topic. 
./out/producer
You should see output resembling this: 
Produced event to topic: ID = 890243:0:2, key = awalther   value = batteries
Produced event to topic: ID = 890243:1:2, key = htanaka    value = book
Produced event to topic: ID = 890243:2:2, key = jbernard   value = t-shirts
Produced event to topic: ID = 890243:3:2, key = eabara     value = gift card
Produced event to topic: ID = 890243:4:2, key = htanaka    value = batteries
Produced event to topic: ID = 890243:5:2, key = htanaka    value = book
Produced event to topic: ID = 890243:6:2, key = awalther   value = t-shirts
Produced event to topic: ID = 890243:7:2, key = awalther   value = t-shirts
Produced event to topic: ID = 890243:8:2, key = sgarcia    value = book
Produced event to topic: ID = 890243:9:2, key = awalther   value = gift card