12 weeks shred, question about routine

I just bought the 12 weeks shred package and I have some questions. It doesn't specify how many warmup sets I should do. Any advice?
Secondly I don't understand how the sets are constructed, it says; for example 8-12 reps and above this it says stop 2 sets before failures.does this mean is should do more then 12 reps if I can or if I make 12 reps should I increase the weight to the point that I don't make it to 12 reps?

Hope someone understand what I'm trying to explain.