Ever wonder what that crazy-looking button on the upper right corner was?
That is the widget and desktop customization menu. It allows you to change desktop settings, add/remove widgets and lock them, configure shortcuts, and even change the zoom of something.
KDE uses the Dolphin File Manager. It could have easily used Konqueror, which is what a number of older versions did, and it basically looks the same. Except it's not a web browser, even though it looks like one.
Speaking of Konqueror, this is the Konqueror web browser. It can do a whole lot more, and is actually a really decent browser. It works much along the lines of Chrome and Safari.
The network manager is pretty straightforward.
It would appear as if you can add more panels and widgets, just like GNOME. However the interface and means by which to do so differ greatly.