Ok. Let's say you want to make a forum nice and easy using phpBB. Let's assume that the forum will be hosted in a subdomain of your site like this forum.mysite.com.
First of all, enter the c-panel of your website and create the subdomain.
Then visit here to download the phpBB latest version.
Assuming you’ve downloaded and decompressed the files for phpBB, everything you need to upload should be in the directory called phpBB3. The only real requirement is that the directory structure be preserved.
Use your favourite FTP program (I use filezilla) to upload the folder's files to your subdomain. It will take a while, so go make a coffee or something and white until the uploading is done.
Now, it's time to prepare your database in your server. Open the c-panel, create a new database and give it a name, ie. my_forum.
Create a new user and add it to the database (giving it all privileges).
Ok. Now it's time to start the installation. Enter the URL into your browser to open the installation screen. The first time you point your browser to the URL (http://forum.my-site.com for instance), phpBB will detect that it is not yet installed and automatically redirect you to the installation screen.
Press the 'install' tab, then the 'proceed to next step' button and then the 'start install' button.
You now have to decide which database to use.You need:
The Database Type – the database you will be using (e.g. mySQL, SQL server, Oracle)
The Database server hostname or DSN – the address of the database server (write 'localhost' in our example).
The Database server port – the port of the database server (most of the time this is not needed).
The Database name– the name of the database on the server (write 'my_forum' in our example).
The Database username and Database password – the login data to access the database.
After you have entered your details, you can continue by clicking the Proceed to next step button. Now, phpBB 3.0 will test and verify the data you entered.
If you see a "Could not connect to the database" error, this means that you didn't enter the database data correctly and it is not possible for phpBB to connect. Make sure that everything you entered is in order and try again. Again, if you are unsure about your database settings, please contact your host.
Now you have to create your administration user. This user will have full administration access and he will be the first user on your forum. All fields on this page are required. You can also set the default language of your forum on this page. In a vanilla (basic) phpBB 3.0 installation we only include English [GB]. You can download further languages from www.phpbb.com, and add them later.
That's it! Just press 'proceed to next step' button until 'login' button appears. Click it and you' re done!
Don't forget to delete or rename the installation folder of phpBB in your server!