Generate a key with:

ssh-keygen -t rsa

When you are entering the values for the key, remember to set the name and path appropriately.
Upload the public part to your server using:

ssh-copy-id -i ~/.ssh/root_key.pub root@1.2.3.4

Whatever you set the name and path to in the ssh-keygen part you will need to make sure it replaces the ~/.ssh/root_key bit in the second command.

Now you can use rsync to seamlessly copy files from one computer to another

rsync -avz --progress /home/person1/DirectoryOrFile person2@1.2.3.4:/home/person2/DirectoryOrFile

…so that’s:

rsync -avz --progress  username@server: