I'm 16 and I've been thinking about having sex with my girlfriend for awhile now: she is ready, I'm still deciding but I think I will with her eventually when I'm ready. When we do there is no doubt in my mind that I will use a condom and I already have one but I really dont know much about them because everything I hear from programs at school or whatever is don't have sex, sex is bad, you're not ready, etc. I never hear anything about having sex but with a condom really I know there is a chance of the condom breaking but exactly how big of a chance are we talking about here because a 10% chance and a 90% chance are two totally different things. Also is there a way for her to get pregnant if the condom doesn't break? I don't know how that would be possible but that's why I'm asking because I don't know, also can stds be transmitted while using a condom even if it doesn't break?

First up, good onya, J, for thinking about these things in advance, despite that fact that you've been so unprepared to do so by your community!

Here's the scoop on condoms for you.

• Effectiveness & Use: With perfect use, condoms are HIGHLY effective, around 98%. Perfect use means a few things. It means using condoms EVERY TIME you have genital contact or intercourse, without fail, from the start of that contact until finish. It means applying them correctly: click here for those instructions, and instructions are also always on the boxes of condoms you buy. It also means -- stated or not on boxes -- using some extra latex-safe lubricant with the condom to keep it moist and flexible, even if a condom already has a little bit of lube on it. You can get lubricant at the same places it's best to get condoms: pharmacies, grocery stores or online merchants (avoid buying condoms in places like gas stations, because they've often been on the shelf for a while). It means using only good quality condoms within their expiration date, and never using a condom twice: it's one condom per act of intercourse, only.

  When a condom is used perfectly, there is only a very small chance of pregnancy. If that's more of a chance than you or she are comfortable with, then you can back up your birth control with a second reliable method and make that chance as close to zero as it gets. Condoms are the only male birth control besides sterilization, so that means a backup is something she'd need to pursue by talking with her doctor or sexual healthcare provider.

  Without that perfect use, condoms are more like 80 - 85% effective. So, using them right is really key. You'll also want to have more than one when you are ready for sex. It's easy for people to be tempted to go without when there aren't enough around, and you might accidentally try and unroll that one backwards -- in which case you'd need to use a new one -- or have that one start to slip off, drop it while you're putting it on, any number of things. So, people using condoms as birth control and/or safer sex really need to have a bunch handy at any given time.

• Breakage: When you use condoms perfectly, as described above and at that link, they are very unlikely to break. To review, breakage is prevented by being sure to put it on correctly -- being sure to leave room in the tip -- by using good quality condoms, stored properly, and by being sure to use extra latex-safe lubricant with them (which also makes condom use far more pleasurable for both partners, as an extra bonus).

  If and when you do ever have a condom break, and it is the only method of birth control being used, your partner has the option of using emergency contraception, which she can get via a prescription from any doctor. If she likes, a woman can even ask to have a prescription already written to keep on hand just in case that happens. That's a great idea, since EC is only effective within the first 120 hours of a risk, and the sooner it's taken, the more effective it's likely to be.

• Condoms & STIs: Condoms provide AWESOME protection against STIs (sometimes also called STDs). With infections and diseases spread by body fluids -- semen or vaginal fluids -- it's nearly flawless protection. The protection condoms provide against a couple STIs -- namely, HPV (genital warts) and Herpes -- aren't as good, but condom use still reduces transmission of those infections by 70% or more. So, when it comes to preventing disease and infection, it's a win-win with condoms: without them, those risks are high, especially amoung 16-22 year-olds, who have the largest number of STIs of any given group.

Hopefully, that gives you a better start in understanding how they work and having the info you need to have on hand when you get closer to that point. Obviously, feel free to explore the rest of the site for all sorts of other information, and once more, kudos for thinking about this in advance!