When what looked like a very bright light flew across the sky, the people didn't take it as a warning that aliens would be landing on earth. When the thing that we call an alien comes to the earth he shows up saying that his people wish to make friends with the earthlings.
He is much taller that a normal man. His head seems to show that he has a huge brain. He never speaks by opening his mouth, but by a machine. So really it shows that his race is much more intelligent than the human mind.
They argue about if they should trust the aliens or not. They also try to decipher the book that the book that he left behind. After a long time they believe that the title of the book said "To serve man." They do some test to see if his body will react like a humans, and to see if he was lying.
He promised to help end hunger, and war, and he did just that. Now some of the human race will visit the alien race. Well that is what they thought but it turns out that the title of "To serve man" is actually a cook book.