References :
https://www.howtogeek.com/howto/ubuntu/install-samba-server-on-ubuntu/
https://www.linuxbabe.com/ubuntu/install-samba-server-ubuntu-16-04
https://www.howtoforge.com/tutorial/samba-server-ubuntu-16-04/

0) Get root
$ sudo su
1) Install the binaries
$ apt install samba system-config-samba
2) Create a share
- backup the config file
$ cp /etc/samba/smb.conf /etc/samba/smb.conf.bak
- edit the file
$ nano /etc/samba/smb.conf
and add a section like this at the end of the file :
[Private]
path = /samba/private
browseable = yes
guest ok = no
writable = yes
valid users = @samba
3) setup the samba group, user and permissions
$ addgroup samba
$ useradd smbuser -G samba
$ smbpasswd -a smbuser
$ mkdir -p /samba/private
$ cd /samba/
$ chmod -R 0770 private
$ chown root:samba private
4) Restart the samba server, you should be good to go
$ systemctl restart smbd nmbd
5) Try it from a linux client
e.g. in Linux Mint, file browser > File > Connect to a server
Server : the IP address
Type : Windows share
Domain name : WORKGROUP   # unless you changed this in /etc/samba/smb.conf
User name : smbuser
Password : the password set up for smbuser