Sandbox and Production environments
A Sandbox environment is used for Testing and Development. Sandboxes are completely isolated from your Salesforce production organization, so operations you perform in your sandboxes do not affect your Salesforce production organization, and vice-versa.
Any new enhancement is first developed in Developer Sandbox then moved to Test Sandbox for Testing and when feature are all green to go, they are moved to Production for business to use it.
SmartClient provides the options to launch into your production account directly or you can access the sandbox environment first.
After launching the app, you need to connect to Salesforce account.
After you connect to the Salesforce account, you have the option of accessing the sandbox or production account.
Select any of the option and access the app using your credentials.
The above example shows access to the sandbox environment. You can connect up to nine sandbox accounts.
Accessing the accounts through Account Settings
Select the account of your choice
Go to Settings and find this screen.
Click on the icon to alternate between YES and NO.