OMGsh!! Biology

Biology is hard for me. even though its easy for others i have yet to catch a grasp on it. On certain things i can catch it and understand it but sometimes I'm still lost even after you have explained it to me two and three times. Well, im trying and im hanging on for dearlife. But i do know that there are so many different ways to prove the beginning of this world but, which one is true. Is it the big bang theroy or God made the earth or did we revolve from monkeys. The natural gases and carbons prove one thing and a book proves another and scientist and human acting animals prove another. Which one is it?