Question about getting citizenship.?

I have a friend who parents brought her here to the us when she was little. she graduated high school. She was going to go to a college, but didn't end up getting the scholarship she applied for. She really wants to go to school. But has no idea on how to become a us citizen. She can pass the test they give no problem. She just wants to know how much she'll need and after she turns in the naturalization n400 application what happens? She keeps reading about this biometric thing. What is that please help she's already gone to the website just needs more info. Thanks