What's a sandbox?
A "sandbox" is your personal wiki page where you can practice editing, plan out articles, draft articles, or just experiment, without impacting the article "mainspace” on Wikipedia—which is what we call live articles.
To go to your default sandbox page, simply click the sandbox link, which can be found at the top right whenever you are logged in.
Think of your sandbox as a replica of a blank Wikipedia article. All of the same tools are available for you to use.
Anyone can still see your sandbox, so it's important that the content you put there isn't something you don't want people to see.
Don't copy and paste things there that might violate copyright rules.