Yes, it's true that apart from stars, galaxies and planets there are such things as black holes that randomly pop up in space - they're very mysterious objects. What exactly are they and what would happen if you fell into one?
A black hole begins to exist when a star ends its life by exploding and becoming the so-called Supernova. Most parts of the star get scattered into space but other parts collapse upon themselves due to the influence of gravity. Young stars can't become a black hole because there is always a balance between the two forces: the gravity and the pressure of the components of the star. Both of them are equally strong so the star cannot collapse, as well as it cannot stretch itself out. The Supernova explosion is so strong that it causes a huge time warp - and that's our black hole. In other words, there's only gravity left, that's why the old star eventually collapses.
What would happen if you got really close to it? Well, you wouldn't be immediately sucked up into it, although if you reached "the point of no return" (also known as an event horizon), you would never be able to escape, just like light wouldn't. You'd get torn apart by gravity, so you'd never know if a black hole leads to a different universe or some other kind of world, like in sci-fi movies. It's also impossible to see a black hole with our own eyes because it's not really black as they show in the pictures - it's invisible but it causes an effect of the background's starlight deformation, so it's easy to tell if there is a black hole nearby.
If you're interested in black holes, take a look at the sources:
https://www.nationalgeographic.com/science/space/universe/black-holes/
https://www.youtube.com/watch?v=E7W71XFXF0w
https://space-facts.com/black-holes/
Here's a video showing a gravitational lensing effect caused by a black hole:
https://www.youtube.com/watch?v=y30bsSuTAIo
