Do you already have one? Please check the expiration date; it needs to be valid for six (6) months past the end of our pilgrimage. In other words, if it expires before October 11, 2013, you'll need to get a new one this Fall.
Here is the official passport website, which should give you all the information you need about fees, forms and where you can get one.
As part of the process, you'll need a photo. They get pretty specific- you just can't pull one of of Facebook from your birthday party. Most drug stores like Walgreens, CVS, Rite Aid, etc are set up to take passport photos, and if you check their Sunday circulars, they run coupons for them every so often. If you are a member of AAA, you can get passport photos taken for $6 (free for Plus or Premier Members). AAA will also do currency exchange for members without a processing fee... but that's for another post!