Back To The Future begins in the year 1985 where our main character Marty has his life set for him. He's got a great girl that he's about to take out for the night with his dads car. The day the film starts he gets back home from school and his dads boss Biff totals Marty's dads car and ruins Marty's chances with his girl. When the film jumps to the future Marty messes with his parents lives and when he ends back up in 1985 some things have changed. One of thoughs things is Biff ends up doing everything for Marty's dad and the car wasn't totaled it was in fact being polished by Biff for Marty's date. These events happened because when Marty arrived in the future he messed up his parents falling in love by diving into the road and pushing his dad out of the way of his grandfather hitting his dad. That was the moment that his dad and his mom fell in love but instead Marty's  mom fell in love with him. Marty kept a picture of his siblings and himself in his wallet and when he went to look at it his brother started to disappear out of the photo. Marty then went to The Doc because he knew he was the one person that could help him. Because of that one moment across from his mothers house it changed everything which made him have to get his parents together before he disappeared himself. So he tried to take advantage of his mother at a dance so his father could be the dashing hero but instead Biff ended up taking advantage of Marty's mother and his father ended up punching Biff which finally let him stand up for himself. Another thing Marty does to change the future is he writes Doc a letter informing him that he will be shot the day that he goes back to the future and that he needs to do things differently so he can stay alive. Doc gets the letter and rips it up because he doesn't want to change the events that lead to the future. But Doc ends up taping it back together and in the year 1985 he puts a bullet proof vest on that saves his live. The last thing I have to point out is in 1985 Marty's mom is and overweight alcoholic and in the future Marty tells her she shouldn't drink. When we get back to the past Marty's mom doesn't drink that much and shes thin and happy.