MainOOConnect

//Listing 1 Again our starting main Code
int main( ) {
//retrieve an instance of the remote service manager
    Reference< XMultiServiceFactory > rOfficeServiceManager;
    rOfficeServiceManager = ooConnect();
    if( rOfficeServiceManager.is() ){
        printf( "Connected sucessfully to the office\n" );
    }

//get the desktop service using createInstance returns an XInterface type
    Reference< XInterface  > Desktop = rOfficeServiceManager->createInstance(
    OUString::createFromAscii( "com.sun.star.frame.Desktop" ));

//query for the XComponentLoader interface
    Reference< XComponentLoader > rComponentLoader (Desktop, UNO_QUERY);
    if( rComponentLoader.is() ){
        	printf( "XComponentloader successfully instanciated\n" );
    	}

//get an instance of the spreadsheet
    Reference< XComponent > xcomponent = rComponentLoader->loadComponentFromURL(
	OUString::createFromAscii("private:factory/scalc"),
        OUString::createFromAscii("_blank"),
        0,
        Sequence < ::com::sun::star::beans::PropertyValue >());
// add code here
    return 0;
}

This code is called a bootstrap and uses com.sun.star.lang.XMultiServiceFactory, com.sun.star.uno.XInterface and com.sun.star.frame.XComponentLoader interfaces and com.sun.star.frame.Desktop service.

Remember each time you query for an interface you have to add code lines (if they don't exist) in the source code and a line in the makefile. I will generally add comments to prevent omissions. You can find more explanations here (if you are not a beginner).