In many small local area networks, the SMB protocol is used to offer network services. Names like “Windows® Network” or “Windows® for Workgroups Network” or “LanManager” are often used as well. Using SMB you can access so-called “shares” (i.e. folders made available by the server) as well as printers.
KDE comes with built-in support for the SMB protocol. As KDE is network-transparent that means you can access SMB shares from everywhere you can access your local files, for example in the Konqueror file manager and in the file dialog. To make use of this you should provide KDE with some information on your SMB network. But don't worry, this is normally pretty simple as, for example, all the Windows® clients in your network need and have the same information.
For the SMB protocol to work, it is required to have Samba correctly installed.
Although there are a lot of insecure SMB networks out there which allow access to anyone, in principle you have to authenticate yourself to access the services of an SMB server. By default, KDE will use the data entered in the Default user name: and Default password: fields to authenticate itself on SMB hosts. If you leave the field Default user name: empty, KDE will try to access SMB hosts without a username. If you leave the default password empty, it will try without a password. If KDE is unsuccessful accessing the host using these settings, you will be asked for a username and a password.
While it makes things more comfortable if KDE stores your SMB password, this may be a security problem. If you are using SMB in a security conscious environment, you should not store your password here but rather enter it anew every time you need to access an SMB host.