In order to connect your first remote site, you will first need to install and activate the plugin on both the local site and the remote site. See installing and activating the plugin for more information.
Adding a remote site
Once the plugin is installed and activated on both the local and remote sites, you will need to add the remote site's domain and access key to the local site. Head to WP Admin > Settings > ACF Remote Sync and in the Connected Sites field, click the Add Site button:
In the new site row, add the remote site's domain and access key. The access key can be found by logging into the remote site and heading to WP Admin > Settings > ACF Remote Sync. The access key is displayed in the Site Access Key field and can be copied by clicking the Copy button:
Once the domain and access key have been added, click the Update button. The settings page should look similar to the following:
Checking the remote site has been connected
To confirm that the remote site has been added successfully, head to WP Admin > ACF > Field Groups and click the Remote view link. If the remote is configured correctly, all field groups on the remote site will be listed on screen ready for import: