Resting heart rate is a very general indicator of your overall fitness. Lower resting HR typically means you are in better shape. There is no "right" number, but what you should be tracking is trends over time. For example, for me when i am in a training block, my resting HR gets lower as i get stronger. Then when the holidays come and i train less and drink more, you can clearly see a rise in resting HR.

for training paces, look up how to do a basic lactate threshold test. This will help you determine some basic training paces. For example, zone 1 might be anything below 120 bpm. Zone 2 121-140bpm. Zone 3, 141-160bpm.... Etc. Up to your max HR. Different HR zones produce different physical adaptations, so training plans will help you pick the right paces to run at each day. You shouldnt just go out and smash it at threshold pace every day.

If your watch is able to track heart rate variability (HRV), thats another useful metric. It's the variance of time between heartbeats. The heart is not a perfect metronome. Like resting HR, you should track trends over time. HRV is pretty responsive to how your body is feeling. My HRV goes down overnight if i've been drinking. Indicating that my body has been under some kind of stress (in this case, ingesting literal poison)

Those are some basics. Lots of material out there on the internets.