Hi,
You have only one user account create. The link is located in the upper right corner of the Home of Wiki (in German "Anmelden / Benutzerkonto erstellen").
Ideally, you write your article in two languages, so English and Spanish. After you have created your user account and you have registered on the wiki. Home of the wiki can create your article. You write your "Page Title" (please in english) in the input line below the icons and click on the button "Neue Seite anlegen". This will open the WikiEditor and you can create your article.
I hope you have already created items in a Mediawiki ;-)