It is described in Czech https://www.turris.cz/doc/cs/howto/nas or here on forum Samba USB Disk not showing in Windows 10 in english for older openwrt here https://wiki.openwrt.org/doc/recipes/usb-storage-samba-webinterface. But you could google it yourself. It could be all configured within luci.
For FTP server configuration is decribed here https://mihail.stoynov.com/2014/11/22/openwrt-ftp-installation-and-configuration-vsftpd/ you have to ssh or telnet and configure it from command line or use midnight commander to modify scripts. After login to turris commandline by ssh or telnet install midnight commander by opkg install mc then you could use mc command to start Norton Like commander to edit files as it is easier than use Linux command line editors.
Be aware that for both cases you have to adjust you hdd path to your situation and modify commands and scripts according to your situation.