How to add menuel title and description on the frontpage and each forumdisplay.php?fid=x page
i think the googleseo plugin does this automatically
I know but I will rather do it manually if possible.
Having the same meta description and keywords on every page isn't a good idea - you'll need a plugin to have dynamic meta descriptions/keywords.
To add meta description and keywords to the index:
ACP >> Templates & Style >> Templates >> Index Templates >> index
Find:
{$headerinclude}
Add after:
<meta name="description" content="your description" />
<meta name="keywords" content="your, keywords" />
I want to use description that I do - on some specific selected sub-pages - if possible.
This works fine for the main page and some other pages:
<meta name="description" content="your description" />
<meta name="keywords" content="your, keywords" />
But can I do anything specific about page forumdisplay.php?fid=1111 (example)
Not without a plugin, no.