My understanding of it, probably not fully accurate but should explain the basic idea: A black hole is a mass so dense that it's own gravity will not let anything out, including light. If you make the mass small enough (like kilos or a few tons) you can theoretically achieve this by compressing it into a tiny volume (probably on the order of the size of an atom or something). That's gonna have that property, but it is also not going to be stable as it's own gravity can't actually hold itself so compact and compressed, hence the short life span (basically it explodes). Obviously the more mass, the longer it'll hold together, until it's enough mass for it to be stable, at which point it becomes unlimited in life time.

When you see articles that describe how they made a small black hole in a lab, that's what they mean: they compressed matter to an absurd degree, but probably only for nano seconds (if that).