HIV enters the body through cuts in the skin, open sores, tiny tears in the mucous membranes of the mouth, rectum, or vagina, and directly into the blood by a needle. It is generally accepted that the virus is transmitted through direct exposure to contaminated bodily fluids that have not been exposed to the air.
In order to assess your risk in intimate activities, consider the continuum of risk below:
Very low risk -- no reported cases due to these behaviors
Masturbation or mutual masturbation
Touching or massage
Erotic massage or body rubbing
Casual kissing
Oral sex on a man with a condom
Oral sex on a woman with a dental dam
Low risk - rare reported cases due to these behaviors
Deep kissing
Unprotected oral sex
Vaginal sex with a condom or female condom
Anal sex with a condom
High risk -- millions of reported cases
Vaginal sex without a condom
Anal sex without a condom