Training Stress Score (TSS) helps establish a single estimate of the overall training load and physiological stress created by that training session. It is an estimate of the training load created by a workout based on intensity and duration. A 1-hour cycling activity at maximum steady-state intensity is 100 TSS. It can also be used to determine how much recovery may be needed after a given workout.
TSS and Training Stress Score are trademarks of TrainingPeaks, LLC and are used by Intelligent Cycling® with permission.
Here is a video that will show you how to use and find TSS
In the Session Designer, you find TSS and the overall time in each training zone, in the lower right corner.