In short, the recommended steps to manually do the syncronization is:
- (Full/Delta) Import from on-premises directories, such as Active Directory
- (Full/Delta) Import from Azure AD
- (Full/Delta) Synchronization from on-premises directories, such as Active Directory
- (Full/Delta) Synchronization from Azure AD
- Export to Azure AD
- Export to on-premises directories, such as Active Directory
Understanding the steps
The keys to understand the steps:
- Import (step 1,2) imports things from AAD or on-premise AD to the AAD Connect server for comparing purpose.
- Synchronize (step 3,4) doesn’t really make things change. Imagine it as comparing the things that just imported, and find the differences – it doesn’t change anything!
- Export (step 5,6) does make things change.
Behind the syncronization
If you are also interested in the “Run Statistics”, e.g. “Connectors with Flow Updates”, read the reference  below. This document is from an old product FIM 2010, which is renamed as MIM 2016 by now.
Are we talking about “AAD Connect”? Well… I didn’t find a document of AAD Connect about the statistics by now, if you find it, let me know. For now, read the reference  and just for reference.