AT&T Flow Designer is a user-friendly visual tool for designing, prototyping, and deploying IoT solutions by enabling users to visually integrate data sources, cloud services, and embedded devices. It is particularly compatible with PubNub's Data Stream Network, allowing users to trigger device actions, stream sensor data, send push notifications, and track geolocation in real time. The tutorial explains how to integrate PubNub into Flow Designer, demonstrating the creation of PubNub input and output nodes, and the use of debugging tools within both Flow Designer and the PubNub Developer Console. Furthermore, the text highlights the collaboration between AT&T and Hackster.io for the Real-time AT&T IoT Starter Kit Challenge, encouraging developers to create innovative IoT applications using AT&T's IoT Starter Kit, Flow Designer, and PubNub, with the prospect of winning prizes.