Whats the difference between both games in the world of warcraft battle chest package ?

Question

and is the burning crusade free online?

Answer 1

World of Warcraft is the original game. A basic subscription costs $14.99 a month, payed every 30 days.

It has a level cap of 60.

World of Warcraft: The Burning Crusade is the expansion.

This raises the level cap to 70, introduces two new races, and a new region, new instances, and new raids.

Whether or not you install BC, it will still cost $14.99 every thirty days.  

Answer 2

Burning Crusade is the Expansion to World of Warcraft, it adds 2 new playable races a new proffession and raises the level cap to 70 at no additional fee.