In strength training there are three classifications of lifts. The most important exercises will be your primary exercises.
They are the most important because they are what drives your strength and muscle gains. Every workout must begin with a primary lift when energy is highest & muscle exhaustion is lowest.
Purpose: Raw Strength, Muscle Hypertrophy, & Strength Endurance
Exercises: Squat, Deadlift, Bench Press, Row, Lunge, Press, & Pull Up
Accessory Exercises are often misunderstood. The purpose of an accessory lift is to improve your primary exercises. The thought process on adding accessory work would revolve around what specific exercises can I do that will improve performance on my main lift.
Purpose: To enhance performance on the main exercises
Exercises: Can be any exercise with weight; even a modification of a primary lift such as high reps, different grips, and other variations.
Supplementary Exercises are used to increase the performance of accessory exercises. These exercises will be your fine tuning exercises used to fix any muscle imbalances or bring up specific muscles that may be too weak.
Purpose: To enhance performance on the accessory exercises
Exercises: Supplementary exercises can be any movement but will more than likely be very specific. Lateral raises, bounds, single leg hip thrusts, & many more.
Exercise selection can be confusing because everyone is different and the exercise choices you make may not be right for you but right for another person.
Supplementary exercises make Accessory exercises better which make Primary exercises better which make your results better.
Dedicate & Succeed,