BBY/ABY is used to position items along the Star Wars Timeline. BBY refers to Before the Battle of Yavin. ABY refers to After the Battle of Yavin. The Battle of Yavin in Episode IV: A New Hope occured in 0 BBY/ABY.
Star Wars: Adventures in ABC was a book and cassette tape set aimed at younger readers. Each page showed a letter of the alphabet and a character, animal or vehicle whose name starts with that letter, along with a short poem about the subject. The audio tape was co-narrated by veteran voice actor William Woodson and Anthony Daniels as C-3PO.
The book's back cover called it "A Star Wars Adventure in Learning Fun." Another book in this series was Star Wars Adventures in Colors and Shapes.