[Magdalen] Hashtags?

[Grace Cangialosi]

OK, here's another of my Luddite questions:

I keep seeing things that invite one to use #(something), and I have no idea what to do with that. I thought hashtags were used as Twitter designations, and I don't use Twitter, so I've never paid attention.
But recently a friend set up a site where folks can post blessings, and she said to "tag it" with a hashtag name. I told her I didn't know how to do that, and she said I could just comment on her post, and she would transfer it. So I'm still in the dark.