Why do we use init method? [on hold]

I've strong knowledge in jQuery but not in JavaScript (skill level like jQuery). And I want to learn writing a plugin and so I've visited a lot of websites for the tutorials and the great start is Creating a basic plugin to Advanced plugin concepts which gave me a great idea to write the plugins.

So, now I wanted to directly write my plugin using a boilerplate. But I'm stucked with some concepts that I couldn't find anywhere in the wild.

init: Why initialization method is used? And what kind of code should I write here?