Short answer
HubSpot's KB: two-way sync needs Read and Write permissions for each record type in Dynamics 365. Tasks must be associated with another record to sync. You can create Dynamics sales orders from deals or workflows; a line item price changed on the HubSpot deal won't sync to the created sales order. Custom field mappings need Data Hub.
1. Data integration
Sync settings live under data integration in my demo portal.

2. Plan first
Decide which system owns each field before turning on two-way sync.