Making Plugin for IOS

I am trying to create my own plugin for ios platform using ionic. I took help form the cordova’s official site:
The documentation is quite unclear to me, I did follow the steps as in the site, i.e.:
-> created plugin.xml as in the site
-> created a js file with cordova.exec function
-> copied the ios classes from the site
But now I am stuck in how to actually use the function into my controller. Can someone help me?? A step wise instruction set or tutorial for creating a file browser or file chooser plugin in ios??