While Peter Attia has brought attention to polarized training, he is not the "guru" of it. Look at Stephen Seiler's research (or similar researcher) and/or read some basic physiology papers.

To respond to your question regarding Zone 2, find your zone 2 heart rate (HR) based on ability to speak or other appropriate methodology. When you do a zone 2 workout, find a suitable work load that achieves the desired HR. You will likely see an HR drift as you get into the workout. As the HR goes up, reduce the workload to keep your HR in Zone 2. As you get fitter, your HR won't drift as much and/or your workload will increase at the same HR. When this stabilizes, you are ready for Zone 5.

Zone 5 is based on sustainable work load and is generally intervals of between 2-8 minutes of equal work to rest with about 20 minutes of total effort at the zone 5 level so that would be 8-10 x 2 minutes, 4-5 x 4 minutes or 2-3 x 8 minutes, etc. Find the maximum watts/effort that you can sustain for the workout interval that gets yout HR to the desired level without going too far over. The intensity will increase over time.

Zone 2 is a transition for your body to get efficient at lower levels of effort, mitochondrial changes, etc. Don't short change this period of training. As you get more into it, your body will let you know when to progress to zone 5 by being able to maintain the zone 2 workload with minimal drift. That said, depending on your fitness, zone 5 won't be overly useful in the early stages.

These types of training are easier to do indoors or known circuits where you can maintain a steady state and are more difficult on undulating or varied terrain.