Free JSON Resources
The JSON Tutorial at tutorialspoint includes an overview and covers syntax, data types, objects, schema. It also includes short examples of encoding and decoding JSON data using PHP, Perl, Python, Ruby, Java and Ajax.
JSON: What It Is, How It Works, & How to Use It
Pretty much says it all.
JSON Processing (Java)
This is a section of the Java EE 7 tutorial which includes an introduction of JSON and focuses on JSON Processing in the Java EE Platform.
Includes examples that you can run on JSFiddle and see the results.
W3Schools JSON Tutorial