The data export from Spine includes all of the skeleton information: bones, slots, attachments, skins, animations, constraints, etc. You can open the JSON with a text editor and read the data (check Pretty print).
Note if you don't need to read the data, then you should export binary. It is smaller in size and faster to load.
You need the atlas file, PNG file(s), and skeleton data file to load and render your skeleton and animations. The fastest way to display your skeleton data on a webpage is the Spine web player. That displays a single skeleton. If you are building a game then you probably want to use a game toolkit, such as Phaser or Pixi.js.
