Once you're created your Wiki account and logged in, you can find a sandbox area, that is accessible through a link in the upper right hand corner of the page.
In the sandbox you can practice editing and draft changes. Make use of the Sandbox as a new user and then copy your changes into live entries. You can link people to your Sandbox, but it will not be searchable on Wikipedia.
There are 2 ways to practice editing in the sandbox:
Learn more about sandbox editing in the section Editing Basics.