Okay, not to be a dick but that other thread by 3DNa is donkey ****. I will tell you how to meditate immediately without visualizing any complex imagery or levels of frequency or any other nonsense. Keep reading...
The most effective way to meditate (effective meaning brain responsiveness in tests and the users state of being at the time) is with a method called transcendental meditation. It is so simple you will know exactly how to do it by the time you finish these next two paragraphs. Keep reading...
The basic idea of TM is mentally repeating a mantra. What is a mantra? Any word without meaning. Pencil wouldn't be a good mantra, as it has meaning for anyone who knows the English word. Ayinga is a good mantra (eye-ing-uh). You could use any word you want, again, as long as it is a static word that has no meaning to you.
Close your eyes. Being in a quiet room helps but it can be done just as easily in a noisy airport I swear. Give yourself 2 minutes to just sit there, then begin repeating your mantra in your head. Ayinga. Ayinga. Repeat this (or whatever mantra you use). You will often find your mind wondering. This is fine. When this occurs, simply return to repeating the mantra. Do not try to repeat the mantra in a rhythm unless that is how it naturally occurs. Do not try to force anything to happen. You might also find yourself slipping into dreams. This is a sign that you're doing it correctly. A good duration to meditate is 20 minutes, with an added 2 minutes each of "warm up" and "cool down" (2 minutes of not repeating, just sitting there rather)
Benefits? You feel happier. You don't get angry over things that once made you rage. You think more clearer. You feel more energized for your day. I've heard users say it's how to truly reach enlightenment (Indian guy below says it) I know it sounds like I'm trying to sell something or feed you bull****, but try it yourself at no cost...
That's it. Now you know how to meditate. There's a ton of info all over the net with more information, but here is a link with more mantras for now: http://www.caic.org.au/eastern/sydda/free-tm.htm