How to play Online?

So, I wonder if someone could answer how do I play online?

There are a few ways to play online

Dueling Network (DN for short)
http://www.duelingnetwork.com/

Its as simple as sign up, Build a deck and then your good to go!
But this is a manual duelling system so its alot like duelling in real life and requires you to know the rules and apply them yourself.

YGOpro (Percy)
http://www.ygopro.co/login.aspx?ReturnUrl=%2fDownloadmembers.aspx

YGOpro requires your to make a account and then download the duelling system to be able to play. Once your downloaded and installed the system your can make your own decks are use default decks that come with it. The duelling system is fully automated and comes with a AI mode to practise against.

DevPro
http://ygopro.de/en/

Very much the same as YGOpro, It requires you to sign up and download software.
It is also fully automated like YGOpro but it doest come with any pre made decks or a AI mode but it does offer a better social aspect but offering private chat and chat rooms as well as keeping track of your Win / Lose / Draw records.