Read the Introduction in the Darwin text(to find this text go to  http://www.talkorigins.org/faqs/origin.html

and
a) Abstract the Introduction in 5 sentences or more.
b) Discuss the item in the Introduction that you found of most interest to you in 5 sentences or more.
c) Item b above.  Why did you  find this of most interest to you in 5 sentences or more.