Login into ACP >> Templates & Style >> Templates >> Now choose the template you want
Step 2: Find Index Page TemplatesTemplates Click on it and Find index
Step 3: Now at top meaning line #1 where it says below:
Step 4: Replace it with this:
Then press Save And Return To Listing when you go on your forum Left Click On View Page Info and you will see the tag there ,that means it is working.
You can put more meta tags by seperating it with comma , e.g music, videos, game etc