Q: how to have a strong chest

A: The single best chest exercise is the bench press (with either barbell or dumbbells). So the short answer is you build a strong chest by doing bench press. The long answer is that there are two aspects to strength... First there is amount of muscle. More chest muscle will make your chest stronger. The best way to build more muscle is by 'bulking' -- weight training in parallel with intentional overeating to slowly gain weight (the slower the weight gain, the less new fat and more new muscle it'll result in). If you are interested in bulking, start by reading my Nutrition article and Weighttraining article and then filling out Fitness Guide specifying 'Gain Muscle' to get a starter program.

The second part of the long answer is that it's possible to train specifically to increase strength without necessarily trying to increase amount of muscle. This program is designed to do just that -- make you stronger in three most basic exercises: squat, deadlift, and bench press. If you are not interested in squat and deadlift, you could just do the bench press portion of the program. The idea behind this program and others like it is to train your nervous system to more effectively utilize the muscles you already have to lift more weight.