Very often a virtual particle–antiparticle pair appears and because they're very happy they started existing, they immediately hug each other not knowing that will cause them to annihilate each other and disappear.

Every once in a while, the pair appears in a very interesting position: one is outside the event horizon of a black hole (let's call this one Pinocchio) and the other inside it (let's call it 3735928559). Because nothing can escape a black hole, they can't really hug, so Pinocchio says "I'm a real ~~boy~~ particle" and stops being virtual and becomes real, while 3735928559 continues its descent into ~~madness~~ singularity.

Unfortunately, the process means there now exists something (Pinocchio) where there wasn't anything before and that takes energy. And that energy comes from the particle that stayed behind which is now part of the black hole, so it effectively takes energy out of the black hole. You may have heard that energy cannot be created or destroyed, only transformed, that's essentially what happens here.

The Pinocchios go away from the black hole, so they can end up basically anywhere in the universe.

As for the timescales, they entirely depend on the black hole's size. Really tiny black holes evaporate in a matter of seconds, the supermassive ones in a matter of trillions of trillions of trillions of trillions... years.

In fact, black holes will be the last macroscopic structures to exist in the universe because the evaporation is extremely slow - every planet and every star and every gas cloud and every atom will cease to exist long before the last black hole evaporates.

I am not a physicist, but I looked up the answer to this question a few years ago and didn't fully understand but I think it's something like this.

Mass and energy are equivalent. So if it can lose energy then it can lose mass.

Although famously nothing can escape the black hole, energy can be lost via Hawking radiation. I don't really understand this, but apparently quantum particle pairs are always being spontaneously created in empty space. The pair of particles are opposite: one has negative mass/energy and one positive mass/energy. Usually they are randomly created and then instantly destroy each other, resulting in zero net effect. However if this happens precisely on the event horizon of the black hole, then it's possible for the negative mass particle to be ever so slightly inside and the positive mass particle to be ever so slightly outside. So the negative mass particle ultimately falls in, and the positive mass particle escapes. The result is that the mass of the black hole is reduced (by adding particles with negative mass/energy) and some positive energy flies away from the black hole.

This only kinda makes sense to me, because I'd have thought that there'd be a 50/50 chance of the positive or negative energy particle being pulled in, resulting in a net zero effect in the long term. But I think there's some bias to the negative one falling in more often. idk really.

This is VERY MUCH a layman explanation based on something I half-understood a few years ago, so I'm sure people will come along and correct me where needed via Cunningham's Law. But I think that's the jist of it. I suppose if you wanted a fully rigorous scientific explanation you'd have looked it up instead of asking here.

Ace covered it well enough, and I think you can find their "shelf life" using the math Hawking came up with to predict when a certain mass black hole will be fully evaporated. How accurately I'm not sure.

The actual form of the radiation emmited back into space from evaporation depends on the mass IIRC. So stellar to supermassive would show up as photons and neutrinos. As they shrink they get hotter for some reason (I'm just a layperson too) and then could emit stuff like electrons, muons, etc. Evaporation also accelerates as the black hole mass shrinks.

Not sure what happens when the black hole reaches the mass of something that's not a black hole like a Neutron Star. Does the black hole singularity explode? Don't know. That's one idea vs just shrinking until it winks out of existence.