Hey, thanks for being brave! Lots of people wonder about anal sex stuff, but most of 'em don't have the guts to ask.
Anal sex does have some risks aside from the usual safer sex risks, but let me just remind everyone that safer sex practices -- putting a latex barrier between you and your partner so that fluids are not exchanged -- are just as important for anal sex as they are for any other kind of sex.
That means condoms for penis-in-anus penetration, dental dams if you want to lick someone's anal area (yes, people do it, and yes, it can feel really good to a lot of people, so stop making that face), and surgical gloves if you want to put your finger(s) into anyone's anus.
The fortunate thing is this: if you're following safer sex guidelines to begin with, you shouldn't have any problems at all with any of the specific risks of anal sex. How convenient!
The anus and rectum (your anus is the opening, the rectum is just inside), obviously, are going to be a really good place to find the kinds of bacteria and microorganisms that you would normally find in feces. Some of these can get you good and sick if they get into your bloodstream or another person's, and some of them can cause nasty infections. These include a microorganism called giardia, which can cause nasty gastrointestinal infections, and the common bacteria e. coli, which can make you sick with a flulike infection that can occasionally be fatal.
The way to avoid 'em? Don't get them into your body. Just like any other STD.
Some people feel comfortable with anal stimulation / penetration without using gloves as long as they make sure their fingers are smooth, their nails are trimmed very short and filed very very smooth, and they have no visible breaks in the skin, like hangnails or paper cuts. I tend to recommend against it, but if you do it, you need to make sure to wash your hands thoroughly, preferably with an anti-bacterial soap, before you touch your or anyone else's genitals, mouth, eyes, or nose.
The goal, again, is to avoid spreading microorganisms around.
That said, enjoy yourself and use plenty of water-based personal lubricant (no, not spit... that's not safer sex!). The anus does not produce its own lubrication when it is stimulated, and you don't want to give anyone a literal pain in the a** by doing something without adequate lubrication. Wet, Astroglide, KY Jelly, et cetera are your friends.
And just in case anyone's wondering, anal sex guidelines are the same for men and women. Everyone has a butt, and they're all basically the same.
Associate Editor, Scarleteen
"Be Excellent To Each Other" -- Bill and Ted