Hi,
Please look at the user guide located in the installation folder (eg. C:\Program Files (x86)\DHI\2012\MIKE Zero\Manuals\MIKE_Hydro\MIKEHydro_UserGuide.pdf) and look in section 1.5. Section 1.2 - 1.4 are also usefull for a first overview of MIKE Hydro.
Best regards
Oluf (DHI)