I have copied the whole of the terminal - wasnt sure if i had put previous commands in right

dave@dave-laptop:~$ ls /media
cdrom  cdrom0
dave@dave-laptop:~$ 
dave@dave-laptop:~$ sudo mkdir /media/external-ntfs; sudo mount /dev/sdb /media/external-ntfs; ls /media
[sudo] password for dave:
mount: you must specify the filesystem type
cdrom  cdrom0  external-ntfs
dave@dave-laptop:~$ ls /dev/sdb*
/dev/sdb  /dev/sdb1
dave@dave-laptop:~$ sudo mount /dev/sdb1 /media/external-ntfs; ls /media
cdrom  cdrom0  external-ntfs
dave@dave-laptop:~$