There are plenty of tasks that you can do on Wikinews, but by far the most important one is writing articles. New stories are the lifeblood of Wikinews; without a constant supply of them, the project would simply not function. So, while there are other ways to help out, we strongly encourage, firstly and foremostly, writing.
Just like in a real, physical news workplace, the newsroom is the centre of activity. There, you'll see a list of all articles that are in development, as well as those that are ready for publication. But more on that later.
This tour assumes that you know at least the basics about editing a wiki. If you're completely new to the Wiki model, you may want to read this useful guide to editing and this navigation help page. You don't need to read everything in those pages to know how to edit; just skim through to get a general feel for things.
In any case, all basic editing controls are self-explanatory, and you should find your way around without difficulty. Whatever you do, don't be afraid - there's nothing you can do that can't be undone or that will hurt the wiki.
