He saw a multitude of very poor boys who play and blaspheme. A Man of majestic appearance told him: With meekness and charity you will conquer these your friends; and a Lady just as majestic added: Make yourself humble, strong and robust. At the right time you will understand everything.

The years which followed were given direction by that dream. Son and mother saw in it the indication of a way of life.

He was highly gifted spiritually, physically and intellectually, and the best students of the school flocked around him. He founded what was known as the Happy Club. At 20 years of age, John Bosco took the most important decision of his life: he entered the Seminary. There followed six years of intense studies after which he was ordained priest.

He becomes Don Bosco

On June 5, 1841, the archbishop of Turin ordained John Bosco a priest. Now Don Bosco (in Italy the family name of the priest is preceded by Don) was finally able to dedicate himself full time to the abandoned boys he had seen in his dreams. He went to look for them in the streets of Turin. On those first Sundays—says young Michael Rua, one of the first boys he met in those first months, Don Bosco went through the city to become aware of the moral conditions of the young. He was shocked. The outskirts of the city were zones of turmoil and revolution, places of desolation. Unemployed, sad and ready to do anything adolescents caused problems on the streets. Don Bosco could see them betting on street corners, their faces hard and determined, as if to get their way at any cost.

Near the city public market (Turin had a population of 117,000 inhabitants at that time) he discovered a real market of young workers. The part near Porta Palazzo, he wrote years later swarmed with peddlers, shoe polishers, stable-boys, vendors of any kind, errand boys: all poor people who barely eked out a living day after day. These boys who roamed the streets of Turin were the wicked effect of an event that was throwing the world into confusion: the industrial revolution. This started in England but it soon crossed the English Channel and made its way to the South. It would bring a sense of well-being unheard of in previous centuries, but it would be at a very high human cost: the labour question and the gathering of great number of families below the poverty line in the slums of the cities, coming in from the countryside in search of a better life.

Don Bosco spent his life in the service of these poor and often abandoned young people and founded a religious congregation, now known as the Salesians of Don Bosco, to continue his work.

(Source:  http://www.ewtn.com/library/MARY/DBOSCO.htm)