Assuming your setup is something similar to have a single Linux server that acts as a file server for your local lan, with little to no security allowing all users access to the files and read / write access is sufficient.

By now most would have been able to setup Samba and force the user / group and permissions for creating files there may be a need to update the permissions on the files to ensure that all users have read / write access to the files.

find . -type d -exec chmod 775 {} \;
find . -type f -exec chmod 664 {} \;

These two lines will be sufficient to grant the permissions for all authenticated users to the file share to read and write to all directories and files.