Sandbox is a test area. It allows an admin user to test out an import before finalizing it to the live account. Think of it as a practice run, Your data is placed here first so you can see what everything will look like before you save it to your live account.
If you import data, and find out you did some things incorrectly, or some fields didn't translate the way you expected, no worries – while you're in Sandbox, you can wipe the pending import and try again.
If you need help importing data, read our importing guide, Using the Import Wizard.
When you're in Sandbox
You know you are in Sandbox when there is an addition bar at the top of the page, labeled in the top left Sandbox.
Some features such as filtering (on pages like Contacts and Activities) are not needed when viewing data in this test area, and aren't enabled while in Sandbox
We recommend checking 15-20 contact or transaction records against your source data (the CSV you imported) to verify the data was mapped and imported correctly
Back to Account (in the top right) will return you to your live account
Wipe Sandbox (in the top right) will clear out all data in Sandbox for you to perform another test import
If you're still curious how the Sandbox plays into the import process, here's a roadmap of what importing looks like.