Heart rate Training Zones can be used during cardio vascular training.
Just to point out, that using heart rate to measure intensity of a strength training workout seems a little odd. Heart rate is a measure of cardiovascular output/intensity, whereas strength training is neuromuscular.
Anyway, to know what heart rate zone you should be working at, you will need to know two things:
your max heart rate and training zones
There can be many ways to workout out your max heart rate, with popular ones such as "220 - Age" (then use the percentage intensity) and the Karvonen Formula. The Karvonen Formula includes your resting heart rate.
Karvonen Formula Example for a 50 year old, with a resting heart rate of 60bpm and wants a moderate workout.
220 - 50 = 170
170 - 60 = 110
70% of 110 = 77 + 60 = 137
80% of 110 = 88 + 60 = 148
Target heart rate should be between 137-148 bpm
You might use each zone during different phases of training and depending upon your training goal. For example, you might use zone 1, where intensity is light as a warm up and/or as a recovery session. And you might use zone 5, where intensity is hard for some speed work (intervals).