Glad to have found this post. I needed something reasonable to respond to for post count.
That said, you've got to have a webserver installed. If you're looking for a simple way to install MyBB - I'd recommend that you use VertrigoServ. It's free.
Download it for Windows, run the installer, and then in the tray area of Windows, right click on the server icon and select the WWW folder.
Put all of the MyBB files in here.
Next create a database by right clicking on the server icon again, going to PhpMyAdmin.
Create a user account. Then create a database.
Now navigate to localhost in your browser: 127.0.0.1
You should get the MyBB setup prompt. Use the username for the database that you created above with the same password and database name. Click install and it should setup and work.
Well, you need a way to manage your SQL database so unless you know SQL, phpmyadmin is going to be your easiest solution. If you're on Windows, an easy way to get a webserver set up is WAMP, and if you're on Linux, try checking out XAMPP.