Changing window managers will make major changes to the look-and-feel of all your windows and it is not advisable to do unless you are sure you understand the consequences. Doing it on a machine supporting a vendor-enhanced one may lose all of the vendor-specific features like floating toolbars and icons. In some cases applications will crash if you use a window manager different from the one intended by the software vendor. Many window managers allow you to customize settings with a configuration dot file that should be put in your home directory. If the window manager is called foo, this configuration file is typically called .foorc and templates called system.foorc which you can copy, rename and customize are usually located somewhere in the window manger distribution tree (see documentation for details). You might also want to look in the dotfiles locker for ideas on how to customize settings.
In a number of cases, the window managers support correct basic functionality but utilities and program launchers may not be configured or present on Athena; consequently attempts to launch these using window managers controls may fail. Some window managers may start processes that can add significantly to your cpu load. These may need to be killed manually if you decide to switch to another window manager.
Additional information is at the Window Managers for X page.
Window managers are normally started automatically on login provided certain entries are in required configuration files. You should not normally need to start one manually. You do not need to do anything if you want to use the default Athena window manager (metacity for debathena). Due to significant changes in the debathena environment, we do not recommend that you use window managers in the windowmanagers locker or others installed elsewhere, but rather use the optional ones accessible via the Session: button on the login screen only.