It won’t do anything… yet. Or rather, depending on how you store it, it’ll do something you don’t want.
If you store it as plain text, when you scan it, Android should open a popup telling you it’s read something, and - depending on your cellphone - show the text. Or not.
The idea is that, at some point, national COVID certificate checker apps will include the NFC NDEF processing bit that will correctly recognize the certificate text string and decode it.
Right now, none do, but we’re working on it. Or rather, we’re waiting for sluggish EU public servants to leave the coffee room and gp back to their desk to do a tiny bit of work.
Honestly… They managed to approve ONE pull request since I opened mine on Nov 4… At that pace, it’ll be fixed in time for the next pandemic.