Using The OGL
By attaching this license game developers allow the use of their OGC and any additional content they may have indicated to be OGC. This use is perpetual, worldwide, royalty-free, and non-exclusive as long as the use is accompanied by a copy of the OPL with all the Copyrights updated to credit the contributors of all OGC that was used. All used OGC is to be indicated with a notice.
Licensees are prevented from distributing, copying, or modifying PI, and may not use the contributor's name for the purposes of marketing or advertising, unless permission is acquired through a separate license or agreement with the holders of the PI.
Finally, the OGL requires attribution be maintained by the copying of all copyright notices from OGC a licensee is copying, modifying or distributing. This requires that the license notice itself must be altered by adding all copyright notices to the Section 15 part of the license.
Read more about this topic: Open Game License