When you use a external usb hard disk it’s formatted in fat32. NTFS is a better option, because NTFS can manage more big files (backups for instance).
When I buy a external hard disk I format it to NTFS. To get permission to write I use ntfs-config to mount the external drive. After boot the drive will appear in /media folder. To use it as a normal usb drive you may erase the rows in the fstab files created by ntfs-config. After reboot then you can connect the external disk and unmount it like a normal usb drive, and you can write on it.