Unless you work out regularly, you should try to figure out what your level of physical fitness is before jumping into a workout program. This is especially important if you are middle-aged, or if you have health problems that might contraindicate an intense fitness regimen. If in doubt, make sure you clear things with a doctor.
Repetitive reps of push ups while lying on the back with hands tucked to the hind under the shoulders and then gradually pushing up the body up ensuring the back and legs remain straight, are a good starting point. Then chest exercises that strengthen the upper torso such as hand held dumbbell exercises. You can then progress to Latissimus dorsi exercises that aim specifically aim at develop the Latissimus dorsi which include the large side muscles in men that make the triangle-shaped. This are built exclusively using dumbbells. Finally you have to work on the triceps and biceps to complete the upper body exhaustion.