In C for example, a wchar would be a Unicode character. The regular C string functions won't work on Unicode strings, so instead you use the C runtime library functions available for Unicode strings, prefixed with wcs.
Example: wcslen, wcscpy and such.
Of course the C compiler and the runtime library must have support for Unicode if you plan to use it.
You tell the C compiler that you plan to use Unicode through a macro:
_UNICODE // Tell C we're using Unicode, notice the _
Then define a Unicode string:
wchar_t string = L"Ubuntu rocks";
Here is the wchar.h header file.