Samba is a free implementation of the SMB/CIFS protocol which is used to share files and printers in a network. Most modern file managers like Dolphin and Nautilus support this protocol.
You need to mount the share to use it in Amarok. To do this, you need to install the package smbfs. Use the command
sudo mount -t cifs //host/share /mount-point/
to mount the share. After that you can use it like a local folder and add it to your local collection.
The easiest way is to use your file manager. On Debian-based distributions like Ubuntu you can install a Dolphin extension to manage shares using
sudo apt-get install kdenetwork-filesharing
Open the properties of a folder in Dolphin and switch to thetab.
To share the folder, just check thefield and set the share name under the field. Check the checkbox to allow anonymous users access to the folder.
The folder should now be accessible to the network. Please see the Client section for details on how to use it in Amarok.