Letters indicate an exercise group. All exercises with the same letter are performed in a sequential fashion until all sets have been completed. Numbers simply indicate the order of the exercises within a group. Just like reading a book, you will follow the workouts from left to right and then down to the next line. When reading the workouts, you will perform the indicated reps with the prescribed tempo and take the rest period written before moving down to the next exercise in the group. Once you reach the end of a group you will go back to the first exercise listed and repeat the process until you have completed the appropriate number of sets before moving on to the next group. Do not skip the rest periods! The rest periods within a group can have a significant influence on what type of stimulus you will get from the workout. If there are four exercises (B1, B2, B3, B4), doing them one after the other will have a drastically different effect on what type of stimulus is created compared to if you were to rest 60 seconds between each exercise.