It's all in the title. How can I give an object health?

You can create your own Integer Attribute, or use the built-in 'health' Integer Atrtibute (you need to toggle it own via: 'game' Game Settings Object -> 'Features' Tab -> the 'health' check box option)

here's a step by step walkthrough guide on creating your own demo game, on the basics of Attribute usage:

http://textadventures.co.uk/forum/quest/topic/5387/i-really-need-help#37375

ask if you need any help with it and/or got any questions about anything