The number of warm-up sets depends on the target load for the athlete in a workout. If you are planning to do a Back Squat with a target load of 200 kg today, you will be suggested more warm-up sets than if you are doing 10 kg Side Laterals. The number of repetitions an athlete does per set is up to the athlete. You can also skip the warm-up altogether by entering a target load right away.
Warm-up sets are only calculated if a training target has been set. If the training target is open, everything is considered a warm-up set, unless you mark (long press) a set as a working set. Every set afterward will be considered a working set.