This is the basic steps to export contacts as a .vcf file, import them to Google (aka Gmail) contacts and then send them to another device. It's not difficult.
1. Open the iPhone contacts app and tap Menu.
2. Select Import/export and export your contacts as a .vcf file.
3. Transfer the .vcf file to a computer or cloud storage for upload to Google. Or, upload can be done directly from the phone with a browser.
4. Log into your Google (Gmail) account and open Contacts. If you are uploading directly from the phone with a browser, you will need to switch to the desktop version of the Contacts webpage. You cannot use the mobile version.
5. In Gmail Contacts, click on More. In the drop-down list select Import.
6. In the next box select Browse. Navigate to the exported .vcf file and select it. Click on Import.
7. Once your Google account is added to the S6 just enable synchronization of contacts and you're done. Should be enabled by default in Settings > Accounts > Google > Tap on account > Set sync options.
Be sure that when you add new contacts they are always saved to your Google account.
Android since v1.0. Linux user since 2001.