This is a mod for noita that provides apis to allow them to safely perform tasks that normally required them to be marked as unsafe, as well as some general utilities.
To install, simply download and move the LibNoita folder into your mods folder. Once you have it enabled (Requires unsafe mods to be on) make sure it is at the very top of the list.
Once you have it installed, start a new game and you should see your enabled mods get their own sections listed in the mod settings. Here you can choose what permissions each of them get.
If you let someone borrow your car, you would give them the keys to the car. Not using this mod is basically the equivalent of giving them the whole ownership of the car and making them promise they will give it back when they're done. I'm sure you can see the problem here...
You shouldn't... At least not right away. But that's why it's open source. Having this mod installed greatly reduces the risk of any mod misbehaving and damaging anything. (Except itself of course, if malicious mods want to self destruct by all means go ahead) Any dangerous permissions are completely restricted to this mod and libraries that require them, which means the mod using the libraries need no power whatsoever.