Hello and welcome! Glad to have you "walking" with us. To set my goal, I used google maps to get directions from my address to my Disney hotel (Pop Century). That then became my total miles needed...1025 for me. I wear a pedometer regularly so I just use it to measure how far I walk. I only count the miles done in exercising-type walking (for me it's mall walking, a neighborhood walk or when DD is riding her bike and I'm following along). There are others on the list who count their walking, biking (exercise or road) and eliptical machine miles as well. The choice is yours. If I understand Walk Away the Pounds correctly you know how many miles the walk you choose is, right? If so, just use that number.
Whenever you have miles to add to your progress, come back here and post them. Most of us keep a running total and display it like this...60.3/1025. As of Thursday I had done 60.3 miles of my 1025 total miles. You could also set up a ticker in your signature from tickerfactory.com similar to the trip countdown ones people have. They have a set of fitness tickers too.
Hope that helps! If you have any other questions, please ask. Good luck with your walk!