There are several examples of how he helped people. The story is not very difficult to read. Give it another try, and I'm sure you'll find more than three examples. To get you started, I'll give you one example.
As he is bending down to pet a kitten, he is knocked over by a young woman who is hurrying to get to work. She is already late, and she is impatient with Mr. Johnson for delaying her. He suggests that she let him "buy" her day. He gives her the amount of money should would have earned at work that day. Then he looks over the crowd for a suitable companion for her. When he finds just the man, he "buys" that man's day as well, and he gives them more money for lunch and a movie or any other activity they might choose.
So he helps the young woman not only by giving her the money she would have lost for missing work, but also by introducing her to a young man and making it possible for them to spend the day together.
Now, read the story again and look for some more examples. Hint: pay attention to the little boy who is waiting while the moving van packs up his things.