When you're in Garmin Connect, select an activity which should show the map and your route, along with the data on the left side. Then select "Player" in the bar above the map. You can change the variables in the graph to display power, speed, cadence, etc. When you hit play you can watch the data change on the bottom of the map, or you can select a point on the map or the graph to display the data. It's not a great tool, but kind of fun to play with.