What are Sandbox Pages?
These pages are pages where users can mess around with the wiki pages without messing up the real wiki page that they are working on.
How do they work?
You can copy the contents of any page you want to work on into that page and do your thing to it before putting the changes on the actual page. This can be especially useful for really long pages that you're doing major edits to, and will need to spend several days on.
How to get one?
Each user gets their own personal page in the Ubuntu wiki (after signing up for a LaunchPad account).
To create one
In the address bar, type in wiki.ubuntu.com/ followed by <your username>/sandbox and press enter. You should get a page that says, "This page does not exist yet. You can create a new empty page, or use one of the page templates", on it. On the top of this page, under the "Ubuntu Wiki" banner, there is a botton called, "Edit". This botton allows you go into editting mode where you can work on the page that you need without messing up the real page. Make sure you save this page when you are done editting it!
NOTE: Beware that someone else may make changes to the page in question while you have a copy of it in your online sandbox. You'll want to compare the current contents of the page with your contents for the page when you're ready to replace them. it's highly recommend to use Meld for this, and it's available in the package manager.