If you are applying for a passport for the first time you must apply in person. If you are under the age of 16 you must also apply in person. If your current passport was issued more than 15 years ago or your passport was lost, stolen or damaged you also apply in person. If you have legally changed your name and are unable to legally document the name change you must also apply in person.
To apply for the passport you must fill out form D-11 which is the actual application. You mustprove that you are a US citizen generally your birth certificate will be enough evidence. .You will need at least one passport photo the only thing left to do after this pay your fee. Good Luck