What should I do after failing the oral portion of my private pilot check ride?
AOPA has a great article about this, and it basically says:


Since you failed the oral, more studying is probably in order.
You will need to receive training in the area(s) of the checkride that you failed from a flight instructor.
Once the flight instructor feels that you are proficient and able to pass the checkride, they will sign your logbook so that you may take it again.
Schedule your checkride again.  If you take it within 60 days, you will only need to test on the areas that you failed.  After 60 days you have to take the entire checkride over again.
Take your Notice of Disapproval (8060-5) with you to the checkride (you didn't burn it did you??)


Like the article says, it isn't the end of the world!  About 20% of first time applicants fail their checkride, but all you have to do is use it as a learning experience and let it make you an even better pilot.

If you have questions about specific subjects, you can also ask questions here and we will be happy to help you out!