So that first sexual encounter with a new partner approaches? Have you given any thought to what was once euphemistically known as protection? In other words, have you bought your condoms?
First, though, to state the obvious: a condom is a sheath of latex or polyurethane (the latter is useful for those with latex allergies) which fits over the erect penis from top to bottom and contains a reservoir into which the semen is ejaculated when the man reaches his orgasm.
So far, so good. This is barrier contraception, since the condom forms a barrier between the ejaculating penis and the inside of the woman's vagina (or anywhere else the penis happens to be, of course).
If used correctly the effectiveness of a condom as a method of birth control is high, and it offers pretty much total protection from the HIV virus and STIs (aka sexually transmitted infections).
The sad thing is that condoms are needed because people carry infections. You wouldn't think it, would you? But there you are. People carry diseases, and sometimes they don't even know it.
Anyhow, back to the condom. Condoms are made in factories where they are subject to rigorous testing - usually being filled with liquid in quantities not even the most copious ejaculator could match, or being blown up like a balloon to see when they burst. They should, therefore, be pretty reliable in practice.
Unhappily, they do occasionally burst during use, especially if they're being subject to unusual friction. So make sure there's plenty of lube around as you thrust - either her natural vaginal lube or some artificial lube like Probe or Astroglide is fine. Even though some condoms bill themselves as ready-lubed for intercourse, in my experience this isn't much use.
When you unroll a condom onto your penis, there are a few simple rules to follow. You need to squeeze the reservoir at the tip to exclude any air, then you place the rolled-up condom over the glans of your erect penis, before unrolling it down the shaft.
Done as a part of sex play, this can be very exciting (it means: you're about to get some pussy!). Problems will arise if you get the condom inside out (it won't unroll), so check it's the right way round first, and if she's putting it on you, make sure she's practiced first. Indeed, why not get a cucumber and have a practice session together on the vegetable before you try it for real.
If nothing else, it might give you a laugh, and she can always use it as a dildo if she's feeling excited.
I mentioned lube. An important thing to remember is this: DON'T use any oil-based products to make your sex slippery, as it will degrade the condom faster than even a premature ejaculation can fill its sperm reservoir.
You can use oil with polyurethane condoms, of course, since polyurethane doesn't have the same sensitivity as latex.
In case you're in any doubt, it will say on the box if a condom is made of polyurethane, so only use oil if you see the word polyurethane. For example, don't get any massage oil onto the condom if you've been having an erotic massage session.
Thankfully these days modern technology has delivered unto us ultra thin condoms whose sensitivity is very high and in which your penis won't be deprived of much of its sensitivity. I should add, though, that condoms do reduce a man's pleasure during sex: that's a fact, and you have to live with it if you want the protection that goes with the barrier.
The question arises - would a thinner condom mean a man was just as aroused during intercourse as if he wasn't wearing one, and, if so, would he ejaculate normally, or would he still have a slightly lower level of stimulation due to the condom, and would that help him to slow down, last longer during sex, ejaculate later, and therefore act as a kind of premature ejaculation treatment? Feedback would be helpful here if you have any experience in the matter!
What else? Well, if you happen to be a premature ejaculator, you can find condoms with a mild anesthetic coating. This may make you last longer, but it will also numb your penis, and if the anesthetic is on the outside of the condom, it may well give your partner a numb vagina too. She'll not thank you for that.
Once you've done the deed, you need to remove your penis from her vagina before it goes limp, keeping a good hold of the condom so you don't leave it behind, ready to leak out the semen.
Other thoughts: don't try and reuse a condom; don't keep them near heat; don't use one if it's past its best-before date; and if you can't face the clerk in the store, buy them on-line. But why you should be embarrassed is a mystery: almost everyone has sex, you know.
What of the vexed question of size? Well, you certainly need a condom that fits your penis, since if the condom's too big it may slip off, and if it's too small, it may feel uncomfortably tight around your penis. It isn't true that one size fits all. You can get much more information here on the size issue:
An interesting prophylactic product is the female condom. It fits inside a woman's vagina and is held in place by a flexible ring which sits outside her vulva. (It's better than it sounds, honestly). The great advantage is that a woman can take responsibility for her safety as well as his. I've never tried this, but it certainly could be a good way of enjoying more natural sex - the female condom is made of polyurethane and it feels much more natural than a latex condom on your penis.
Finally, to all you women out there: don't allow a guy to persuade you to have sex without a condom. Sure, it can be difficult: you fancy him, you don't want to lose him, he tells you he's tested and clean, etc, etc. No way. Use a condom. He might be lying just so he can get sex from you.