If you wish to experiment, you are free to play around on a Test page.
However, the Test page is a public page, so if two or more people are simultaneously using the page, it leads to conflict.
Instead of using the public Test page you can create your personal Sandbox in which to learn how to use the Wiki and to work on articles you wish to create and contribute to the Wiki.
As a first step, you should have chosen a user name and logged in.
Whenever you are logged in, your user name appears at the top of any page on the Wiki.
Click on your user name to visit your personal User page, and then click on the Edit tab.
You may now provide biographical or other information about yourself and your interests.
But in order to create a sandbox, write this link code on the Edit screen: [[/My Sandbox]]. When you finish editing your User page, click on the Save button at the bottom of the Edit screen and you will be returned to your User page where your Sandbox link will be at the top of your User page. From then on, you may at any time click on that link to go to your personal Sandbox and use it for learning Wiki and for working on articles you want to create and contribute to the Wiki.