NewBe In Symbian OS (Help Needed !!)

Dear All,

   I have be assigned the work which is totally diffrent from my previous
   work,

  I wanted to know the basic diffrence between the Symbian OS
  and Win32 OS.

   For example diffrence between the file mapping in the win32 OS
   and Symbian OS.  such as Open the file,  Read The file, Size of File,
   etc........

    So I want the related document / and links from where I can get the
   Info about the diffrences between the Symbian OS and The Win32 OS,
   So that I am able to map these file/etc operations in Symbian.

    Thanks in Advance
     Ranjeet.