How to make an MMO

how can i make my game multiplayer and online...like world of warcraft and runescape etc.

Here's a couple of links you should read first:

If you haven't created a complete single-player game, yet, you should probably also read the following resources:

please start with the tutorials here.

http://unity3d.com/support/resources/
And if you have a specific problem, post your code and problem here. Currently, your question is way too broad to be answered.

theirs also photon server which is free also unity has it’s own networking.