To have the share up and going, for Windows clients, or Unix / Mac clients running SAMBA you need to...
#1. Install / mount the drive. This is done in services --> USB, and it sounds like you have this part done, the volume mounted at /mnt/.
#2. Create a SAMBA share that works on your domain / workgroup. This is done under services --> NAS.
Make sure you set up the share, and users / passwords (assuming you are using a workgroup / homegroup.)