Can someone Explain Mutex and how it is used?

I read a few documents about Mutex and still the only Idea I have got is that it helps preventing threads from accessing a resource that is already being used by another resource.

I got from Code snippet and executed which works fine:

#include <windows.h>
#include <process.h>
#include <iostream>
using namespace std;


BOOL FunctionToWriteToDatabase(HANDLE hMutex)
{
    DWORD dwWaitResult;
    // Request ownership of mutex.
    dwWaitResult = WaitForSingleObject(
    hMutex, // handle to mutex
    5000L); // five-second time-out interval
        switch (dwWaitResult)
        {
        // The thread got mutex ownership.
            case WAIT_OBJECT_0:
            __try
            {
                // Write to the database.
            }
            __finally {
            // Release ownership of the mutex object.
            if (! ReleaseMutex(hMutex)) {
            // Deal with error.
        }
            break;
        }
            // Cannot get mutex ownership due to time-out.
            case WAIT_TIMEOUT:
            return FALSE;
            // Got ownership of the abandoned mutex object.
            case WAIT_ABANDONED:
            return FALSE;
        }
    return TRUE;
}

void main()
{
    HANDLE hMutex;

    hMutex=CreateMutex(NULL,FALSE,"MutexExample");

    if (hMutex == NULL)
    {
        printf("CreateMutex error: %d\n", GetLastError() );
    }
    else if ( GetLastError() == ERROR_ALREADY_EXISTS )
        printf("CreateMutex opened existing mutex\n");

    else
        printf("CreateMutex created new mutex\n");

}

But What I don't understand is where is the thread and where is the shared resource? Can anyone please explain or provide a better article or document?