Can someone explain the Obama birth certificate controversy?

His Kenyan grandmother ( father's mother) said he was born in Kenya. When a person is born in another country to an American citizen under the age of 19 that makes them a citizen of the country they were born in, not an American citizen. Obama's mother was under the age of 19. Right after having him she flew back to the US and got a birth certificate in Hawaii. Obama ordered the Governor of Hawaii not to release his birth records.