I need help on writing a paper about Bernal Diaz Del Castillo?

I have to write a paper on Bernal Diaz del Castillo. Any little information about him is very helpful. I need to know how he was exactly, like a bio? Why did he write his book, The conquest of new spain? The theme fo the book and what his conclusions were? Why did he go out on an adventure with spaniards? And why were the spaniards able to defeat so many Aztecs?