Two kinds of information can flow through ports: data and events.
For the Refreshed at Time port, the data is the time — the number of seconds since the composition started running. At the moment the screenshot above was taken, the port popover showed that the data was about 12.87.
The port popover also shows that the Refreshed at Time port is outputting information at about 60 times per second (the monitor’s refresh rate). Every 1/60 second, the port outputs a slightly greater number of seconds — accompanied by a second piece of information called an event.
Events control the timing of your composition. An event is an impetus or signal that tells a node that it’s time to do its job.
Why are events and data separate things? This will become clear later when you learn about event-only ports and event-only cables, in which events travel without data.
When you run the Quick Start composition, the nodes do their jobs one at a time, left to right. That’s not because they happen to be placed left to right on the canvas, but because the events and data flow through nodes and cables in a methodical way — which we’ll trace through now using port popovers.