To learn about the concept of tidy data, I highly recommend you read the chapter "6 Data Tidying" from the book "R for Data Science" by Hadley Wickham and Garret Grolemund.
To learn about the concept of tidy data in the context of text data, I refer you to the chapter 1 "The tidy text format" from the book "Text Mining with R" by Julia Silge and David Robinson:
