Assuming that you have configured your
/etc/samba/smb.conf file to allow "everyone" appropriate access to your share, you can use the following parameters to control file/directory access:
create mask = 0755
Similar to the numeric format used by
chmod, a "create mask" of 0755 will allow files created by your users to have full access to their own files. Everyone else will only have read and execute access, but not write access. Note that the default is 0744, which allows full control for the owner, but only read access for everyone else.
directory mask = 0755
While "create mask" only works for files, "directory mask" applies the same logic to directories. Of course the particular setting of 0755 (full control for owner, read+execute for group and others) is the default.
Although dated, this link offers a more-detailed description of these options, as well as a breakdown of the meanings behind the numeric values (should you require that).