http://en.wikipedia.org/wiki/Vasco_de_gama

Question

Your guess will be as good as anyone's!! Read the section called Early Life.

Other websites with not much more information:
http://www.google.com/search?q=vasco+de+gama&rls=com.microsoft:en-us:IE-SearchBox&ie=UTF-8&oe=UTF-8&sourceid=ie7&rlz=1I7SUNA

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WHY DID VASCO DA GAMA EXPLORE

In addition to the above answer please consider the following.

Your teacher in asking the question about Vasco DeGama could have one or both of the following ideas in mind expected outcome of the answers.

Idea # 1 Vasco De Gama was a great explorer in his own right. I visited Portugal several years ago and was surprised to see the large number of monuments to him in that country. Just about any place in Portugal has remembrances of Vaso DeGama. If memory serves me correctly a major bridge out of Lisbon (the capital) is named for him. He is a national hero, very much in the same way that Columbus even today is honored by Italians and Italian Americans. In the sites already provided to you can determine some of he reasons for his voyages and the importance of India to Portugal and Europe.

Idea # 2 In class you probably will be studying the motivations of the discovers, explores and conquerors.
Usually the motivation for the explores are summarized by the phrase "god, gold and glory" Think about which ones apply to Vasco DeGama and then to others in the Age of Exploration.

I hope that this information is helpful.