Riders who aren't used to tracking power sometimes want a more familiar benchmark to put their ERG workouts in perspective. Zwift's "Training" mode is one solution. In this mode Fliiiight will create the resistance for the ERG workout you've selected, while in the simulation you move across the virtual course based on your power, just like when you use a powermeter with a simulation. Be prepared for the total disconnect between the resistance provided by the trainer and the course on your screen!
Note that virtual speed and distance aren't measurable without a virtual course.