What kind of share do you want? Do you want to create a directory, that is shared on the network or a directory that is shared between local users? If the network share, then use Samba. In the second case, you need to set correct permissions to the directory you want to share,  but i don't know how to do it. Whatever I've tried, the second user cannot access the shared content while it's in the same group and the group has permissions to read/write the directory and it's contents. What i didn't tried is to set rw permissions for everyone else, but i don't want that.