You don't have one, you say? My, how disappointing. Well, I know how easy it is to trivialize something to which you cannot relate, so I'll do my best to put it in words you can understand.
Let's start by preparing the womb--I mean, your testes. For the purposes of this experiment, your testes will be known as the Human Development Chambers (HDCs). Every four weeks, your HDCs begin the process of interior decoration. They're hoping to welcome a live-in guest, you see. They put up soft, squishy wallpaper and install even softer carpet. They spend three whole weeks making everything perfect for their guests' arrival.
When the fourth week comes, your HDCs are shocked to realize that no guest has landed on the doorstep. They become angry, and in a fit of rage they begin ripping up the carpet and slicing off the wallpaper. They hack it, they tear it, and they begin sending it down the Evacuation Tube (along with a lot of blood) straight into your underwear. Congratulations! You've just gotten your period.
You can expecting this state of ranting and dropping chunks of wallpaper down the tube to last for approximately a week. Of course, you're still expected to work and carry on as usual. Stick that pad in your underwear and go about your day with a smile, pretending you don't have several pounds of tissue and blood building up between your legs. Don't forget to use the bathroom at least every two hours, so you don't have any unfortunate leaks and spoil your favorite jeans! And you might have to change your sheets three or four times.
With all this turmoil happening in your lower regions, naturally your brain gets irritable and distracted. You forget things. Your lower back aches in sympathy. You scream at your significant other for forgetting to buy chocolate. And whenever you express anger or frustration--even if it's totally justified--your friends wink knowingly at each other and brush it off with, "Is it That Time again?" If you dare to mention your condition to your female friends, they respond with, "Gross! Don't talk about that!" or, "Whatever; it's just a period. All men get them."
When the tirade from your HDCs is finally over, you breathe a sigh of relief. Don't worry, though--they'll start decorating again right away. And since the whole cycle takes four weeks (not one month), you can expect it to happen thirteen times every year for approximately thirty years of your life.
There are a couple of ways to avoid your period, of course. You can go in to a clinic and have your reproductive system surgically removed, but then you run the risk of being rejected by potential life partners who want children. Or, you can allow yourself to get pregnant. You might even think that being pregnant is totally worth not facing a bloody mess every four weeks.
So you get little babies growing inside, and for the first few weeks you don't notice much. Then suddenly, dear God, you are starving like you haven't eaten in fifteen years. You gobble everything in sight, and then you realize that your body won't tolerate it. All the food you ate comes right back up. You can expect this to go on for about three months, while your HDCs (and their protective covering) grow to the size of potatoes. Your jeans don't fit, and you start wearing sweats a lot.
For the next three months you're mostly okay on the nausea front, although you're still eating enough for a Tyrannosaurus Rex. The doctor tells you this is normal, although your HDCs have now swollen to the size of cantaloupes. Even your sweats don't fit now. You have to buy special clothes which are freakishly expensive, and everyone comments on how "cute" you are.
The next three months see your HDCs increasing to the size of jumbo watermelons. "How is this even possible?" you wonder. You worry that your body won't be able to support the weight. You need yet more new special clothes, and your significant other groans as they take out their wallet. "More clothes? Can't you make do with what you've got for the next two months or so?" You try to make them understand that you genuinely can't fit into anything, so unless they want you to go out in public naked or wearing a blanket muumuu..
And finally, finally the day arrives when your sweet little babies are to make their appearance. You have the option of having a doctor slice you open and remove them, stitching you up afterward, or of pushing them centimeter by centimeter out the Evacuation Tube over the course of several hours. You'll probably still need stitches if you choose the latter. Whichever way you go, finally you have your precious little ones and it is so worth it. Your insurance allows you a whole two days to recover in the hospital before you're sent home. You know you'll have a few months before you have to face The Period again. And then, with all your sensitive bits still swollen and aching, your significant other asks:
"So, how soon can we have sex again?"