For those who are still new to the game, you can actually make a backup of a Minetest World you have created and this can act as a real backup if you have done some mistakes on the first world.
Here's how you supposedly do it. First you need to find the world file and then find the corresponding folder that has the name of your world and then you make an archive copy of it like a Tarball of some sorts or just use ZIP. After that just enjoy and hopefully you put that world in a USB for safekeeping.
There are other tools that make this rather easier, but I will search it on YouTube, cuz I found it somewhere that said some snapshot something...