How to use these paces
Tempo pace or "T" pace is typically the pace you can hold for about an hour. Tempo pace improves your running economy and form, not to mention that it builds confidence in your ability to hold a strong pace for a good amount of time.
VO2 Max pace is about your 10K pace and a great place to work intervals when training for 5K and 10K races.
Speed pace is a little faster than 5K pace, so when doing intervals at 5K pace, you may want to add 10 - 20 seconds to the pace. This pace is great for doing shorter intervals, 400's to 800's.