Manifests
A manifest is a file that defines your pack to Minecraft. It stores all sorts of important info about your pack.
Like all other code files in your pack, it's written in JSON [Java Script Object Notation].
JSON Syntax Rules:
Data is in name/value pairs;
Data is separated by commas;
Curly braces hold objects;
Square brackets hold arrays;
Every { must be closed by }, every [ with ], same with {}, [], "", ''.
You can learn more about JSON here.