Got a HR monitor now what

I got a Polar FT4 HR monitor form my b-day.

So far I have done two workouts.
1. Post-hole in 2 ft of snow: 32 min, 104 avg HR, 180 max HR, 118 cal, 12 min in zone
2. Walk/run: 52 min, 139 avg HR, 164 max HR, 346 cal, 16 min in zone

What does it mean? Which workout was better? Any tips on how to use the monitor to improve fitness? Should I focus on Max HR, time in zone, or duration of activity?

Replies