A few decades ago, building an application was difficult and time taking. Programmers have to create every single feature from scratch. whereas now, our applications are almost built using external code. This code is usually imported from libraries that are mostly made by the open-source community.
The concept of libraries is amazing, it allows you to build android applications faster. Even build complex features without going deep into fundamentals. Though, it also comes with lots of security risks.
In the fast world, speed is given priority over security. Learning the use of some libraries can help you become a better android developer. Therefore, I would recommend you to learn about a few popular libraries.