How to Create a Forum For My Website?

The majority of web-sites and blogs have a forum (discussion board) to allow their customers and users discuss some topics in there I wanna create one too how can I do it for free?

You have two choices free AKA open source forum script/software or a paid one!

Paid: Vbulletin
Free: MyBB

It' pretty easy to install just create a database in your PHPmyadmin then upload the script and run the installation follow the steps to install

It really depends on your web host, and what environment your in. Typically I've always used MyBB as its free and I like the features and templating system it uses. Another popular one is PHPBB but I think the UI is atrocious so I've always steered clear of it.

If you wanted to go the paid route as @maya said vBulletin is one option, I however have preferred IP Board.

If you need help setting up a forum feel free to shoot me a PM and I'll give you a hand.