You have the option now of applying for either a passport or a passport card but they do not necessarily cover the same things. One major difference is, you can't use the passport card for international air travel. Another difference, the passport card can be a lot cheaper. Check here for the difference between a passport and a passport card.
If you have applied for a passport before, you can apply online.
If you haven't applied for a passport before, then you can download this form and must apply in person.
To find out what facility to go to, search here.
You will need to present one of the following proofs of citizenship below:
Previously issued, undamaged U.S. Passport
Certified birth certificate issued by the city, county or state*
Naturalization Certificate or Certificate of Citizenship
*This MUST be a birth certificate from the state with an embossed, impressed or multicolored seal with the state registrar's signature. Copies of birth certificates will not be accepted.
This is not a legal, authoritative summary and is only intended to provide assistance in the direction of online government passport resources.