Simply add this to your /etc/samba/smb.conf (if it's not there, try searching for it with
find | grep -e "smb.conf"
There should already be several entries like this, but here is a model one for unauthorised sharing. (this is my media directory)
The stuff in [] is totally up to you, it's the name under which windows computers are going to see your directory.
Code:
[MEDIA]
path = /mnt/media/
guest ok = yes
case sensitive = no
msdfs proxy = no
guest only = yes
wide links = no