Here is the opening paragraph of the book:
When I stepped out into the bright sunlight from the darkness of the movie house, I had only two things on my mind: Paul Newman and a ride home.
This lets us know that Ponyboy was walking home from a movie. The reason that he was at the movie alone was because he is the only one of his crowd that really enjoys movies. Ponyboy is the dreamer, the book reader, the sunset watcher of his group - his brothers and friends are not concerned with these things. In addition, Ponyboy didn't want company because he didn't want a distraction - he likes to sink into the movie and live the life of the characters:
When I see a movie with someone, its kind of uncomfortable, like having someone read your book over your shoulder.
On his way home, Ponyboy notices a Red Corvair trailing him. Because he is alone, the Socs have identified him as an easy mark. Five Socs get out of the car and confront him, and the situation looks very dangerous for Ponyboy, but the others of his gang show up and run off the Socs.
This scene lets us know that Ponyboy is a bit of a dreamer and likely to get into trouble because he doesn't always think about his situation. This scene also foreshadows Ponyboy's and Johnny's confrontation with the Socs in the park.
Ponyboy was walking alone because everyone else was too busy to be with him. On his way back the Socs came and attacked him. They used a knife to leave a scar on his forehead too.
Ponyboy was walking alone because everyone was busy so he had to go by himself to watch a movie. He was attacked by the Socs while walking back.