To copy a file using SCP from a remote host you can use the following
scp -r username@111.111.111.111:/home/remotedomainfolder/public_html /home/localdomainfolder/public_html Then enter the password when asked
username is the username of the remote host
111.111.111.111 should be replaced with the ip address of the remote host or domain
/home/remotedomainfolder/public_html is the folder you are copying from
/home/localdomainfolder/public_html is the folder you are copying to locally
If you want to copy just a single file like a tar.gz archive then you can remove the -r and add the filename as follows
scp username@111.111.111.111:/home/remotedomainfolder/backup/siteback.tar.gz /home/localdomainfolder/backup