Being thick again.

I can add info for the internal pages but how do I add description and meta tags for the front page?

Hello,
make sure there exist a record in Manage URLs, where SEF URL is just "". (empty string) - you shoud see it when using filter "Show links to homepage".
If it does not exist, you need to create it. (to non-sef URL put the definition for the home menu item, in our site case, it is e.g. index.php?option=com_content&lang=en&view=frontpage&Itemid=1)

Then you can edit metadata for it as for any other page.