What is a good way to start off a paper?

For my Psych class I am writing on Harry Harlow’s Surrogate Mother Experiment involving rhesus monkeys. If you are interested, you can read more here

Anyway, I am completely unsure on how to start it. I can get it done in 30 min – an hour, if I can get it done. I usually don’t have this much trouble with papers, but this one has me beat. I’m not asking you to write my paper, just give me some advice.