This depends on whether your system is configured to use "ifup" for networking, or "Networkmanager". A PC would normally use "ifup" to start the network config at boottime, a laptop would use the Networknanager since the user will establish a connection whereever he comes by himself.
You can check the settings in Yast - Network - Networksettings
With a default KDE install particularly if you're installing on a laptop, Network Manager should be installed by default.
If that is the case but Network Manager isn't running, at least check whether it can be invoked and maybe not configured to startup and display in the tray by doing the following:
1. KDE Application Launcher Button > Run Command... > "knetworkmanager" (without the quotes)
2. If the Network Manager icon then displays in the tray, lft-click "Manage Connections"
3. Click "Other" in the left navigation pane
4. Check "show tray icon" if it's not already checked