Exercises
Human body evolved with the much physical toiling and therefore has been acclimatised it, thus making physically intensive work the best exercise for human body. But since work no longer physically intensive, humans have to incorporate into their lifestyle a system of physical activity called 'exercises' or 'workouts' that mimics physical toiling.
An ideal exercise system should condition both mental and physical faculties of an individual (since body cannot work without the mind), improve the co-ordination between them, work with human kinetics instead of working against it, give human body the work it needs, and enable an individual to perform day to day tasks with ease and without exhaustion. Rare are such exercise systems; and of those that conform to these specifications, none are perfect or comprehensive. Ultimate fitness can be achieved only through the practice of all forms of exercise systems.
Good old running, physically intensive sports, dance, martial arts, body weight training and yogasana are examples of exercise systems that conform to the natural movements of the body. However, weight training with barbells, dumbbells and machines does not. You may learn more here.
Stay away from the perspectives that the health and fitness industry propagates. A person's fitness, confidence, beauty and sexual prowess does not lie on the size and definition of muscles, or in a lean body, or in the abdominal packs, or in a particular body shape. Some associate physically appearance with confidence. This is foolish because beauty is a factor that is not particularly in one's hand, only its maintenance is; and anchoring your confidence on something that is not in your hands is stupid. Such thoughts come from an uneducated mind. Also, the person must be truly under-confident so much so that he or she now has to find an external entity to boost the confidence. What you are is your mind, the body is merely what it says — a body for your mind. Beyond the aspect of visual aesthetics, there is significance to physical looks.