MrNice

The term "blow-job" is really incorrect. Oral sex being performed by a woman on a man is technically called fellatio.

It involves taking the man's penis in the woman's mouth and stimulating it with her lips and tounge. It can involve kissing the penis, licking it, sucking on it, moving ones head up and down (simulating intercourse) and a variety of other actions. It can also include similar actions on the man's testicles.

It doesn't involve "blowing" on or into the penis.

It usually (although not always) results in the male reaching orgasm and ejaculating. Some women are comfortable having the man ejaculate in their mouth other women do not enjoy this and will ask the man to tell them before ejaculation occurs and will usually masturbate the man to ejaculation. Some women who allow the man to ejaculate in their mouth will swallow his semen and others will spit it out. Any of those options depend on what the woman is comfortable with.

To avoid any risk of transmitting STD's the man should wear a condom during oral sex. Whether the woman swallow's his semen or spits it out there is a risk of becoming infected should the man have an STD.