Migrating your contacts is a two-stage procedure that involves first exporting them from your previous system, and then importing them into the Cloud server.
Sign in to your Google account, go to Google Contacts, and open the Main Menu (top left of the page).
From the main menu, choose Export.
Select vCard (for iOS Contacts) and click the Export button.
Go to the Address Book in Thunderbird (Tools menu > Address Book).
From the Address Book Tools menu, choose Export….
Choose where to save the vCard (*.vcf) file, and select vCard as the file type.
Your contacts are exported to a single vCard (*.vcf) file.
In the Cloud server Contacts app, click on Settings at the bottom-left corner of the page.
Click on Import into and select a local vCard (*.vcf) file.
Done!