A sandbox environment (Preview) is a non-production instance of Financials. Isolated from production, a sandbox environment is the place to safely explore, learn, demo, develop, and test the service without the risk of affecting the data and settings of your production environment.
Additional documentation regarding a sandbox environment can also be found here: https://docs.microsoft.com/en-us/dynamics365/financials/across-how-create-sandbox-environment
To create a sandbox environment:
You must have a subscription to Financials to be able to create a sandbox environment. There can only be one sandbox environment per subscription. You can also reset your sandbox environment at anytime back to the original environment.
In the sandbox environment, a brand-new tenant has been created. This tenant is loaded with default demonstration data for the CRONUS company. No data is copied or otherwise transferred from the production environment during the sandbox creation.
You can use the Sandbox environment to enable Advanced functionality in the Dynamics 365 for Financials and Operations, Business Edition (currently known as "Tenerife"). To do this choose the icon, enter Company Information. Set the User Experience field to Advanced.