Depending on whether you've selected to turn Sync on with the "Sync Future Changes" (Read-Only) option or "Sync Past and Future Changes" (Read/Write) option, the initial steps of your Sync integration may require additional time to complete before you see activity on the. The length of time required depends upon the Systems you have integrated, as well as the number of Records you have in each System.
When you first turn your Sync integration on it performs an indexing of all Records in your End Systems. This is done so Sync can cache and "normalize" the data for each Record visible to Sync. This "Read Only" part of the process does not involve actively syncing data between the systems during this process. If you selected the "Sync Future Changes Only" option no Records will be written until the next sync run that occurs with changes detected in your End Systems. Otherwise, Sync will then move on to processing any updates or creates in each of your Systems as configured by your Field Mappings and Workflows.
You will know that your initial sync is complete when you see your Recent Activity indicate that Sync is Up to Date.
Sync is now in a steady-state and should process any new or updated Records based on the configuration of your Workflows and Field Mappings and display that activity in your Recent Activity Feed.