A display manager is a graphical interface which manages everything related to your session: login, password, generally appearing at the end of the boot process. This interface is clearly more user friendly that just the command line being prompted…
While just the shell prompt is ok for headless servers, a PC user will enjoy Linux via a graphical interface.
If there’s a cool thing with Linux, it’s all the possibilities one can have to customize the interface. You can decide which environment you like most, find some really complete ones or very lightweight ones, it’s really up to you to decide which one you like most.
The display manager – so the login interface – can also be customized: you can install a very simple one with a minimalist design for an old machine for instance or implement one with a cooler UX. It’s up to you to decide.
You can tweak it by modifying it with SUDO rights the following file:
sudo vi /etc/X11/default-display-manager
Once opening it, you will have something like:
Just modify the end of this script line to switch from kdm (KDE) to gdm (Gnome) or to others such as lightdm.
If you chose KDM, you can configure and choose then amongst all the available Themes by looking at :
Applications > system > preferences > KDE
and selection the theme you like most or feel comfortable most with.