I have had an awful time working with KDE widgets - so I'm trying to help you with them! I'll add more articles later.
You've just built an incredible KDE widget, and you want to share it with the world. But how do you make sure hundreds of people will get to try your new widget?
The best way to publish a widget is through the KDE Store. Opendesktop hosts the KDE Store, so first you'll need to make an account with them. Go to the KDE Store and click "Register" in the top right corner. That will take you through the process of creating an account. Once you have an account, go back to the main page of the KDE Store, and log in if you need to. If you click on the profile picture in the right corner, you should get a menu that looks like this:
Click on Add Product, which will take you to this page:
Fill in the information for your app, using "Plasma Mobile Widgets" as the catagory. When you've entered all the needed catagories, press next. We can skip the settings step, so just click next again. Add your .plasmoid file, and click save.
That's it! If you go back to the main page of the KDE Store, search your app name and it should come up.