Here are the prerequisites for using FileZilla with key-based authentication:
Enable SSH access
Generate an SSH public/private key pair
Configure FileZilla (Automatic configuration)
We would recommend using the automatic configuration file for FileZilla as described in the third article listed above. Go to "File" > "Site Manager" and apply the following changes:
Set the protocol to SFTP - SSH File Transfer Protocol.
If you are not using the automatic configuration file, set the Host to your domain name or your server name (listed in your welcome email).
Add your key file (you should click Browse next to Key File, list All Files, and select the private key).
When connecting for the first time, you will get a prompt regarding an unknown host key. You should tick Always trust this host, add this key to the cache, and click OK: