To train your muscles well, you should first train the muscles outside your arms (triceps brachii), hold the dumbbell in your hand, palm down, and then slowly rise and fall. Remember it's slow. If you move fast, you will become a strength type instead of a bodybuilding type. You should know the movement direction of the muscles inside your arm (biceps brachii) and do the same.

Legs and abdomen:

Sit-ups+kicking+turning+starting from both ends.

Pectoral muscles:

Push-ups, three groups, each group of 25-30, a few minutes apart, depending on your ability.

It would be nice to have these three muscles.

In fact, it should be noted that there is a difference between muscle training and strength training, just as the muscles of weightlifters are not obvious, and the strength of bodybuilders is not obvious, which lies in aerobic exercise and anaerobic exercise.