Hi Kabel,
I don't believe it's logical or helpful for hackers on a hacking board to try to pass ethical judgements on attack vectors or the people who ask about them, so I'm just going to give you a straightforward answer.
To DDOS you cause a large amount of traffic from multiple (i.e. distributed) sources to be directed to a target. The target could be an individual, a website, a production server, whatever.
You usually identify the target with its IP address. Most websites' IP address can be obtained with a ping. For example in Windows cmd prompt, OS X terminal, or a Linux command shell just type "ping hak5.org" to get the IP of this site. Some sites try to hide their IP addresses, but you can still sometimes get them with special "resolvers". In the case of an individual, you might send them a link to your website, then check the logs for their IP after they visit.
There are mutliple forms of traffic you might send -- UDP, SSYN, GET, POST, Slowaris, etc. Your options will depend on the software you're using to co-ordinate your DDOS attack and which one is best will probably depend on the set up of your target's computer/server.
So now the questions are where do you get your distributed sources and what software do you use to co-ordinate the attacks. The sources could be your own servers/computers, a bunch of friends, or computers that you control because they are infected with a trojan/virus that gives you control. The software that is used to control them is usually called a "booter" by the younger generation of hackers. It's extremely commonplace that kids own, rent, and trade these booters on other popular hacking forums.
Now, having answered your question as directly as I could, I will throw in a few editorial comments here at the end. DDOSing is an extremely easy, yet powerful, form of hacking (it's so basic it's almost hard for pen tester's to consider it hacking). There are only very limited ethical uses by most people's standards -- you could use it to test the security of your website, you could use it to kick your buddy offline during a multiplayer game bc you're both kids and you know that he has a sense of humor, or you could use it to stop some evil power such as if radical fundementalists had an anti-American website that had to go.
It's caught a lot of negative attention from the public over the past 3-5 years though, due to groups like Anonymous having DDOS'ed various government websites in such a way that could encourage the enemies of America to think that we are weak. You don't want to do that and as a result law enforcement, particularlly the FBI, have been cracking down on lots of kids who use booters. They can trace the source of the traffic very easily and from there find the IRC channel used by your booter to "command and control" the sources of traffic, then from there they find your IP address, show up at your house, slam you on the ground, break your ribs, put their knees in your back, take you to a dirty prison, let you become the sex slave of an STD-infected prison gang, and ruin your future by giving you a criminal background.
That amount of paternalist government intolerance is all absolutely horrifying, aborant, anti-American, anti-Internet, and sickening. But it's the way it is and things are just getting worse, so if you experiment with DDOS do so safely. Use it on yourself and your buddies, but don't use it in such a way that will get you into trouble.
Cheers!