Settings are configurable for both the Raspbmc distribution itself and XBMC.
To change the XBMC settings, first go to the System option on the menu and then select Settings. You will now be greeted with the Settings menu, which allows you to change key settings as follows:
To change locale issues, such as your time zone and keyboard layout, go into the submenu entitled Appearance and change it via the International tab
To change playback settings, such as whether to adjust the refresh rate on playback, go into the submenu entitled Video and adjust it in the Playback tab
You can also adjust settings such as screensaver settings by going again into the submenu entitled Appearance and selecting the Screensaver tab
XBMC is highly configurable and the best way of exploring its flexibility is to navigate the menus and learn more about the settings available. A good place to start is http://wiki.xbmc.org/index.php?title=Settings.