What exactly is the MIT License?

I am trying to begin learning to code by myself, and I was doing some research on Edge's JavaScript interpreting engine, Chakra. I saw something about the MIT License and have been researching. I want to get a grasp of how everything works/is organized before I start really learning to code. I found that the MIT License is part of the Open Source Initiative which (if I understand correctly) originated at MIT. What I don't understand is if this license is a requirement for certain types of software, or if organizations like Microsoft simply choose to apply it to things like Chakra because they WANT their software to be open source. If the latter is the case, why does the software need a license to be open source? Is it to prevent organizations from making false claims that people are using their software without permission?

​

Sorry for the noob question, I just like to understand all the why's before I dive into something. Thanks!