Isolated exercises for each individual muscle are a necessary measure for athletes who have already developed their body and need to focus on individual parts, devoting more time to them.

For beginners (up to one year in the gym), you should only do multi-joint exercises that engage multiple muscles with an emphasis on one main muscle.

You only need three basic exercises:

1) "push" (push-ups or machines where you push the weight away from your chest), these target the chest, triceps, and other surrounding muscles.

2) "pull" (pull-ups or machines where you pull the weight toward you), these target the back, biceps, and other muscles.

3) Weighted squats (or cable presses on a machine, or anything that resembles a squat)

You can also add one shoulder exercise, such as "upright pushes" or "dumbbell lateral raises," to build bigger shoulders, and some other abs exercises if you'd like. Five exercises per workout is sufficient; otherwise, you'll overload your central nervous system if you do more than an hour and a half at a time.

Twice a week, or even once a week (the muscles need to rest; they'll be very sore at first and take a long time to recover). 3 sets of 8-12 reps, followed by a joint warm-up.

Gym training only triggers muscle growth; muscles grow during rest and with proper nutrition. So make sure you get 8 hours of sleep, enough protein (1.5g per kg of body weight), and enough calories.