Adding Facebook OpenGraph Meta tags

Hello,

when I try to share my site (narwhalgarden.com) on facebook, it redirects to “narwhalgarden.com/the-garden” (the url of the first page/section). Obviously, I want to be able to share a customized image/description/url when posting the url to facebook, and don’t want it to just share the first section page instead. I have been trying to find where to add opengraph facebook tags. it seems they should go in the themeheader.php, but nothing changed when I added them.

Thanks in advance!