Crescendo automatically communicates with Box/Google Drive/Sharepoint/OneDrive/Salesforce and initiates a sync when you open the app while connected to the internet.
You may also force immediate sync by either of these methods:
Enter the Command Center and tap on the Update button
With two fingers, double-tap anywhere on the screen
Inside the Case, use pull-to-refresh gesture.
When you initiate a force sync, the activity indicator at the bottom of the screen will be triggered.
Read this post to learn more about sync.