You can add plugins to your project so that you can extend many features in Unity as well as improve your own efficiency and workflow processes. Essentially, Plugins access third-party code libraries, system calls, and other Unity built-in functionality.
These plugins are usually platform-depend (Win, Linux, Mac, Android, iOS, WP, and so on) and might be written with glue-code to allow calling specific OS level functions (APIs) that Unity doesn't provide access to through its classes. Those plugins are oftentimes also written in different programming languages like C/C++, Obj-C, C#, Java, and so on Moreover, the plugins folder allows differentiating between platforms by adding sub-folders per platform: x86, x86_64, Android, iOS, and so on.
We won't cover much 1of these things within our book, so don't worry. Furthermore, they are often easy to implement and use, especially if the plugin is well-done. The key thing to remember is that when you get a new plugin be sure to place it in a folder called Plugins. In this way, Unity will know how to handle them.
Like many other types of folders, you can only have one Plugins folder and it must be placed in the Assets folder. You can refer to the screenshot at the beginning of this section to see this in action.