I have a few of these. Further to what Oli posted, the idea is you’re supposed to scrape off some of the magnesium into a small pile of shavings and then ignite them with a spark from the striking surface (or “flint”).
Used that way they are ok, but good luck trying to do that in any kind of breeze.
I mostly use a Swedish “Light My Fire” now, similar to this
https://lightmyfire.com/products/cookn-fire-collection/swedish-firesteel-2.0/swedish-firesteel-2.0-scout/firesteel-bio-scout-swedish-firesteel-bio-scout-2in1-rustyorange