Watch this video for the basics on how you can use resting heart rate to track fitness and recovery:
Notes:
I track my fitness using a Garmin watch. Check them out here.
Resting heart rate is a quick and easy way to get a GENERAL idea of fitness and recovery. It's not a perfect indicator. It's just one of many metrics that can be used to assess fitness and recovery. To get a more complete picture, you'll want to take into account a variety of different metrics, including HRV, sleep, stress and activity levels, etc.
Lots of things can affect your heart rate on a given day, so its important to look at the big picture and track trends over time.