To create a new article, type the name of the article into the search box on the left and then click on the Search button. When the page is not found, under Search Results the title of your search term will appear as a red link. Click on that link to create a new page.
Go ahead and type in the content and save the result. You can preview your work before actually saving it. Keep in mind that you can always go back and modify it later. All versions of your article will be saved, so that nothing is ever lost, even if you accidentally delete something. This site is based on the same software that powers Wikipedia, so if you know how to use that, you're ready to go.