RIR: Reps in Reserve (RIR) is the number of reps you have left before technical failure after completing a set. RIR allows us to work within a specific proximity to failure and structure a training block with the aim of increasing either weight or reps each week, thus, decreasing RIR. If your RIR and set reps decreases each set during the workout reduce your reps by 1 the following session.
Examples: Your squat 10 rep max weight performed with 3 reps in reserve is 7 reps. If you perform body weight push ups you would perform as many reps as you can until you have three reps left (3 RIR).
Sub Max: Sub max refers to the number of seconds that are left in reserve at the end of each set on isometric holds. Example: If you can hold the movement for 15s max then 4s sub max is 11s holds.
This is a flexible and self-regulated program so it will take a few workouts to get the feel of it and establish proper working sets and reps and this may change (up or down) throughout the cycle and in individual workouts. You are in charge of your fatigue and rating perceived exertion (REP) based off of RIR or sub max holds.
I Marius. I recommend 3-4 RIR for movements that are not core/trunk. Core should be between 1-3 RIR or 4-8s sub max for isometric holds.. IF you are able to hold your RIR/sub max holds stable throughout the sets you have a good rep count and resistance. Hope this is not too generalized (it would be hard to go through the whole program). Let me know if you have additional questions.