Enrolling in a dashboard is easy, simply follow the dashboard link provided and either log in with your Wikipedia credentials. If you haven't already created a Wikipedia account you can also do that now.
The visual editor allows you to edit Wikipedia without using its special mark-up language, instead giving controls that are similiar to a word processor or WYSIWYG editor.
The user page is a Wikipedia page you can create to make a short bio. Your sandbox is where you can practice edits or built pages before they're ready to be put into live Wikipedia.