YaBB is completely free to use. All we ask is that you keep the copyright in tact and visible on the bottom of your forum. This is to ensure that the project and all of the developers are given credit for their hard work. YaBB is distributed under the YPL (YaBB Public License), which is a slightly modified form of the GPL. You can read this license in the Quick Guide distributed with YaBB. If you would like to remove the copyright, redistribute YaBB, or use it in any other non-standard fashion, please consult the Licenses page.
To be allowed to use YaBB, you must keep all copyright notices, both in the script files and all other files, completely intact. You must also keep any license notices provided in the package in tact. Further usage is free, as long as the copyright notices and links to http://www.yabbforum.com remain.
In order to install and setup YaBB, you must first have an existing website. You also need knowledge on how to upload files to your website via a file manager or an FTP client. You should know how to upload files in ASCII and Binary modes and how to set file permissions on your webserver; (such as CHMOD) for read/write/execute access levels. If you want to edit your forum template (and you probably do), you need basic HTML and CSS knowledge
as well. Although not required, having basic Perl knowledge will help you further customize your YaBB forum to your own specifications. Of course, you also need a web browser and a basic text editor such as Notepad++.
System Requirements to Install YaBB