How they have always been is your norm. Have a doctor check your breasts if the appearence of your nipples changed . Palpate them in any way you find comfortable. Do it in the shower, or lying down. Do not leave any part of your breasts untouched.
Breast cancer is very uncommon in teenage years.
Start your breast self-examination in your teens and make it a monthly regular habit. Monthly, about a week after your period begins and the swelling of the breasts diminished. Your goal is to learn the feel of your own breasts, the smoothness or lumpiness when you palpate your breasts. Month after month you want to see if there is any change in their apperance or in their feel. With the help of your doctor and the first mammogram you should learn what is normal for you.