Or renewing an old one, and it's been so long you forget how to do it.
Some of us in the U.S. have been advising each other to get passports, and I was meaning to, but I last got a passport when I was in college, and my mother walked me through it. Also, recent discussions have made it clear there are a lot of socially-anxious people among us, for whom having to ask directions is a major barrier.
The State Department has your back on this; they have downloadable forms and instructions and step-by-step wizards at travel.state.gov. Or you can get a form at the Post Office and take it home to fill out.
If you want to renew a passport, and it was issued less than 15 years ago (so, it expired less than five years ago), you can do the whole thing by mail! Details at the renew-by-mail instructions page
If this will be your first passport, some of it has to be done in person, but you can prepare. Budget about $150 for a booklet-style passport in no hurry.
I just went and applied at my local Post Office. It was $140 to "U.S. Department of State", because I wanted the booklet and the card. Dept. of State will accept check or money order, and I think the Post Office can make the money order for you, on the spot, if you bring cash.
I also paid $40 to the Post Office: $25 handling fee and $15 taking-my-picture fee. They will take cash, check, and I think credit cards.
The application is about two pages, mostly stuff that will be very familiar to everyone who's taken standardized tests. I did have to ask my parents for their place of birth and date of birth.
When you go to get photographed or present your application at the Post Office, expect a line. I arrived at 2:35 on a Friday afternoon, and I got to the head of the line at 2:55.