I have never had sexual intercourse. the doctor told me i had a genital warts infection.i'm was wearing a friend's underwear one day how did i get hpv infection without any kind of sexual activity?

Genital warts can be seen and felt and getting them from wearing a friends underwear would not cause them. You need to see a Urologist. There is an overwhelming chance that if you have had no sex and do not see any growths around the penis head/foreskin area you don't have it.

Some genital HPV infections are unexplained. However, the virus almost certainly is not transmitted by sharing underwear or other clothing. If you have had sexual activity without intercourse (e.g. oral sex) or heavy petting with hand-genital contact, that might be a possibility (although such transmission is rare).