He did not discover America, it was never lost.
Hundreds of thousands of people were already living there quite happly before he went on his voyage, the native indians.
And in fact Europeans had probably already "discovered" it before Columbus went there.
What he did do was to set up a link between Europe and the new world, leading to the eventual development of the country of the USA.
In his journey he was looking for a western route to India (and Asia) and landed on a number of islands (like the Bahamas).
He tought these were part of India hence the name West Indies and the natives he called Indians.
He did four diferent voyages from Spain to the "new world"
See here
http://en.wikipedia.org/wiki/Christopher_Colum bus