On ubuntu 10.04 I know how to share the /media folder by right clicking the /media folder in nautilus, going to sharing options and click "share this folder".

How can I do that from a command prompt in terminal?

You can use the commands chmod and chown to change file permissions and ownership in the terminal. Here are some good beginner guides:
http://www.tuxfiles.org/linuxhelp/filepermissions.html
http://www.tuxfiles.org/linuxhelp/fileowner.html

http://linuxcommand.org/lts0070.php
http://www.linuxclues.com/articles/16.htm
http://www.redhat.com/mirrors/LDP/LD...rmissions.html
I would suggest creating some test files and directories in your /home directory. Fill the directories with useless crap. Then practice changing permissions on those files and directories before you start messing with important data.

Be especially careful if you are planning to change permissions on system files. Under most circumstances you should never have to change permissions or ownership of system files.
Changing permissions on data files in /home or /media is relatively harmless, but practice with test files at first. This is what I did to learn how to do this.

I think he ask about how to share folder on network. It depends which protocol you want to use, you can share by Netbios (Windows method), NFS, sshfs and other. For example for Netbios you need to have installed Samba server and configure it by /etc/samba/smb.conf. In default file are comments specifing how to do it.

Found what I was looking for: the "net usershare" command.