Your AppSheet apps can access data from multiple data sources. Your AppSheet account always has a primary data source used for account authentication (commonly Google Drive) and spreadsheets from that account can be used in your apps. However, you can add other data sources (e.g. Office 365, Smartsheet, Dropbox, Box, and more).
To add a new data source, go to the Account tab where you can examine your current data sources and add or remove sources. Adding a source is as simple as providing authentication.
All data sources in your account are available when you add tables to your AppSheet app. In fact, the same app can combine tables from multiple data sources.