It’s a cute little storybook. Charlie Brown is trying to write a letter, and various Peanuts characters interrupt him, criticize him, and leave him befuddled.
This 1972 hardcover was meant to be a high-end greeting card, with a place in the front to say who it was from, and an envelope that fit it. (This one actually still had an envelope with it, although unlike some volumes that the Pod got in, it was not a Peanuts-decorated envelope but just blank white.) It has a “Dear _____” page in the front, and after that comes the story – 9 spreads, with Charlie Brown’s letter-in-progress on the left page and the Peanuts characters on the right.
These Hallmark minibooks have branding on the back that put them in different Hallmark lines; some are in the Thoughtfulness Library, while this one (like some others) are part of the Ambassador Friendship Library line.