For example, in plain JS, you have to manually update the DOM using DOM APIs for setting styles updating content, etc.
JS frameworks can help automate this repetitive task using features like 2-way binding and templating.
Frameworks have their own way of doing things. For example, Angular is a popular JS framework that comes with many features like dependency injection, routing, etc and has its own way of building an application using it. It is very different from the JS way of doing things. It uses Object-oriented programming and is mainly used by enterprises.
Other frameworks like react are more functional and do not have an opinionated way of doing things. They can be used as part of an application or as a whole for building the application.