I want to get started dabbling in the Bungie API. What can I do with it?

I have seen that you can access all characters of a Destiny account, look at their inventory, and such. I'm a beginner web programmer and I would like to know if there's a way to check individual xp percentages for each armor/weapon in the player's inventory. Also, can anyone point me in a beginner-friendly guide to web programming with an API? I'd like to make my first major web project about a game I'm passionate about. Thanks