Go to http://myeve.eve-online.com/api and follow the instructions.
2) Which API Key do I need?
If you want to see any wallet data then the Full API Key is needed. There is no way to access wallet data on the Eve servers with the Limited API Key.
3) How do I make a feature request?
Either post them here: Eve-Graph - Out of Game Wallet Viewer/Grapher or email: email@example.com
4) Why is my data not updating?
The Eve servers cache data for an hour. Sorry.