Depends, if you're doing largely front-end code (like embedding an iFrame to some chat application) then a widget works best. If you want to modify the API or save things into the database, then a plugin is right for you. I think your best bet is to figure out what you need to do, and then find a plugin that does something similar, and modify that plugin, or take code from it (it's open source afterall ;))

Had half a year to waste because it was too late to switch school level (I'm not even going to bother trying to translate this into weird USA school terms :P), I already knew quite a bit of MIPS (PSP hacking) by then, and wanted to try something else. Don't know why I chose JavaScript, just did. Started with w3schools (ikr), eventually just learned by doing, doing and more doing. Along the way of doing I of course read the occasional article, "guide", best practices, documentations etc. No books and courses though.