An easy way to build AppSheet apps from Excel is to use the AppSheet add-on found in the Office add-in store.
Alternatively, you can also add an Excel spreadsheet to your app by selecting it in the file picker in the app editor. First, select OneDrive or SharePoint depending on where your spreadsheet is located (select OneDrive if you're using data from Office 365).d
Once you have made your selection, the files and folders in your OneDrive/SharePoint account will be listed.
For SharePoint, the sites and sub-sites will also be listed.
While this process is mostly seamless, there are some specific behaviors of which you should be aware.
With Office 365, if a user has the spreadsheet open for editing, other users and third-party apps like AppSheet can't make updates to the spreadsheet. Consequently, if you intend to build an app that updates the data (as most apps do!), please make sure to close the spreadsheet first. Otherwise, you'll see conflict ("409") error messages and the app won't be able to save changes to the spreadsheet.
If using SharePoint, please note that AppSheet can only access files and folders that are stored in the default drive of a SharePoint site or sub-site. Contents that are stored in user-created drives are currently not accessible. In most cases, if you create a file or folder directly in a SharePoint site, the file/folder will automatically be created in the default drive of the site for you. Additionally, if a SharePoint site has been migrated to an on-premises server, it will no longer be accessible to AppSheet.
You can learn more about other data sources here.