How do I mount storage media for btrfs?

I just install urbackup on Ubuntu Linux 17.10.
I want to use a 2TB usb drive for my backup storage.
I formated the drive as btrfs.
/etc/urbackup/backupfolder contains:
/media/BACKUP/urbackup

/media/BACKUP/urbackup contains:
/media/BACKUP/urbackup:
total 12
drwxr-x— 2 urbackup urbackup 4096 Jan 21 15:55 clients
drwxr-x— 2 urbackup urbackup 4096 Jan 21 03:12 urbackup
drwxr-x— 2 urbackup urbackup 4096 Jan 21 16:42 urbackup_tmp_files

/media/BACKUP/urbackup/clients:
total 0

/media/BACKUP/urbackup/urbackup:
total 51408
-rwxr-x--- 1 urbackup urbackup 52428800 Jan 21 03:12 backup_server.db
-rwxr-x--- 1 urbackup urbackup    65952 Jan 21 03:12 backup_server.db-wal
-rwxr-x--- 1 urbackup urbackup    16384 Jan 21 03:12 backup_server_files.db
-rwxr-x--- 1 urbackup urbackup        0 Jan 21 03:12 backup_server_files.db-wal
-rwxr-x--- 1 urbackup urbackup     8192 Jan 21 03:12 backup_server_link_journal.db
-rwxr-x--- 1 urbackup urbackup     4152 Jan 21 03:12 backup_server_link_journal.db-wal
-rwxr-x--- 1 urbackup urbackup    16384 Jan 21 03:12 backup_server_links.db
-rwxr-x--- 1 urbackup urbackup        0 Jan 21 03:12 backup_server_links.db-wal
-rwxr-x--- 1 urbackup urbackup    61440 Jan 21 03:12 backup_server_settings.db
-rwxr-x--- 1 urbackup urbackup     8272 Jan 21 03:12 backup_server_settings.db-wal
-rwxr-x--- 1 urbackup urbackup      391 Jan 21 03:12 server_ident_ecdsa409k1.priv
-rwxr-x--- 1 urbackup urbackup      436 Jan 21 03:12 server_ident_ecdsa409k1.pub
-rwxr-x--- 1 urbackup urbackup       23 Jan 21 03:12 server_ident.key
-rwxr-x--- 1 urbackup urbackup      334 Jan 21 03:12 server_ident.priv
-rwxr-x--- 1 urbackup urbackup      442 Jan 21 03:12 server_ident.pub

/media/BACKUP/urbackup/urbackup_tmp_files:
total 0

How do I mount my usb drive so that it’s used for backups? It looks like /media/BACKUP/urbackup already contains stuff. Is that stuff supposed to end up on the USB drive?

The server documentation doesn’t go into any detail about how to initialize the storage media or how to set up automounts, so I’m stuck.

Thanks for any help you can give.