Use of a memory device context

Question

As I read the memory device context is used to select a DDB object from the memory and draw on it.

Now what i'm trying to do is; select a bitmap object and draw a line on it, would it work that way?

void OnDraw(HDC hDC)
    {
        RECT wnd;
        GetClientRect(m_hWnd, &wnd);
        HDC memDC = CreateCompatibleDC ( hDC );
        HBITMAP memBM = CreateCompatibleBitmap ( hDC, 200, 200 );
        SelectObject ( memDC, memBM );
        LineTo(memDC, 100, 100);
        DeleteDC(memDC);
        DeleteObject(memBM);
    }

I'm confused with what i'm doing here.