Confusion about unit testing frameworks?

So I get the concept of unit testing and TDD on a whole. However, I'm still a little confused on what exactly unit testing frameworks are. Whenever I read about unit testing, it's usually an explanation of what it is, followed by "oh here are the frameworks for this language, i.e JUnit". But what does that really mean? Are framework just a sort of testing library that allows programmers to write simpler/efficient unit tests?

Also, what are the benefits of using a framework? As I understand it, unit testing is done on small chunks of code at a time, i.e a method. However, I could individually write a test for a method without using a unit testing framework.

I'm just very new to testing and unit-testing, clarification on some basic concepts would be great, thanks!