Getting started with joomla API component

Regarding the joomla API component: I've checked the documentation heredocumentation here.

I need plugins to:
Create/edit/remove users and user groups
Create/edit/remove joomla articles and categories
Will also need more after these two, but for now these should be enough for testing.

Is this something you can help with? It's not clear from the docs how to create a plugin.

Thanks for your support!