Install GESync managed package from Salesforce AppExchange:
https://appexchange.salesforce.com/listingDetail?listingId=a0N3000000B5KuWEAV
Note: use default options during install.
Download and install GESync On-Premises or sign up for GESync Cloud.
On-Premises only. Request trial license.
Configure a synchronization profile and start synchronization. Read more in the documentation.