Decided to run a half marathon. First attempt. Not really a runner. How do I start?

Slowly. Go to the book store and skim some of the books/training guides before buying one. Go to runnersworld.Com. Find a local running club - ask at running shoe store. Set reasonable goals first -- work up to the mileage slowly and stay healthy. Complete at least a 5k / 5 mile run well before the half. A 10k would be great preparation. You will get a feel for your body's ability. Train consuming fluids.
Follow a schedule. First, you may want to consider a smaller goal if a beginner runner, such as a 5k. Then, progress to a 10k, then a half marathon. There are many 1/2 marathon training programs online. Choose one that fits your schedule, but i usually recommend a progressive training program over at least a 12 week period, running 3-4 times/week.