A CSV file allows you to pass a list of information (inventory, movies, anything) between different places. CSV files can be created in many popular tools (Excel, notepad, etc) and many programs and websites can read those files.
Title, Director, Year, Rating
"The Shawshank Redemption", "Frank Darabont", 1994, 9.2
"The Good, the Bad and the Ugly", Sergio Leone", 1966, 9.0
As you can see, the first row tells what the list contains, and the other rows are the information broken up by commas (with quotes around text).