The format
The first line usually holds the column names and each following line is a record: name,age then Ann,30. A value containing a comma, quote or line break is wrapped in double quotes, so "Bo, Jr.",25 stays one cell.
Strengths and limits
CSV is simple, compact and universal, which is why it is the default for moving tabular data. It has no types, so numbers, dates and text are all just text until a program interprets them, and it cannot hold nested structures.
Variations
Despite the name, some regions use semicolons as the separator because the comma is the decimal mark. Always check the delimiter and the text encoding (UTF-8 is the safe choice) when files do not open correctly.
Try it
Convert between CSV and JSON with the JSON and CSV Converter, and read how to convert JSON to CSV for the details.
Common misunderstanding
A CSV file is not an Excel file. It has no formatting, formulas or multiple sheets, and opening it in a spreadsheet may reformat values such as long numbers and dates.