Answer by Julian Knight for Denied access to an ext4 partition after doing a `mount -a` command

You should create the folder /mnt/films using the command (in a terminal):

sudo mkdir /mnt/films

Then you need to change permissions so that you have read access to the folder:

sudo chown root:users /mnt/films

This allows group use by the users group which your logged in user should be a member of (it will be as standard). So make sure that the group permissions include read and write:

sudo chmod g+rw /mnt/films

If ther are folders and/or files already on the drive, you may need to adjust their ownership and permissions too.

I assume that you have formatted the drive as ext4? By default it probably came formatted as FAT32.