phpBB is a free forum package (bulletin board system)
How to download and install phpBB
Unpack your forum skin .zip or .rar file.
This .rar or .zip file usaly contain a text file with instructions, photoshop header file, and a .rar or .zip file with your forum skin/style.
Unrar your skin/style file, - DO NOT change the name on the skin/style folder.
Upload the skin/style folder to the folder "styles" inside your phpBB directory on your webserver.
Now you have to install your newly uploaded forum skin/style. Log into your forum board and then go to the Admin control panel.
Click on the 'Style' tab in the Admin control panel.
In the list of links on the left click the 'styles' link which is under the category header 'Style management'.
Now you should see a list of your currently installed styles. You will also see the skin/style you have uploaded into the styles folder which have not yet been installed.
Click Install for your new skin/style.
Once the style has been installed you will have the option to set the skin as default.
(If you set your skin as default it will be the standard skin for you board)