This program is based on weekly linear progress. You take your current 5 rep maxes (5RM) and work up to them systematically by increasing weights in steady increments over 3-4 weeks. You then hit your current 5RM on lifts and continue these incremental increases week to week which pushes you further and further out making new personal records every week until you stall on the majority of your lifts. If you miss reps, keep the weight constant the next week and don't move it up until you get all 5x5. When you eventually stall on the majority of lifts, and you will, meaning something like several weeks of no progress in that you can't add reps or weight, you'll have to reset lower back several weeks and begin again. If it's just one lift that has you stuck, reset on that and work up again but don't restart the whole program.