Windows API basic paint program

Question

Just trying to learn a bit of Win API. I'm trying to make a basic drawing app, a bit like MS Paint.

For the time being I'm trying to get one function to work which is, when you left click and drag the mouse around the screen a line is drawn behind the mouse. Heres what I have so far, but for some reason:

1. The line starts drawing straight away rather then waiting for the left click
2. The line isn't solid its very dotty

The code:

case WM_MOUSEMOVE:
{
    if(MK_LBUTTON){
        hdc = GetDC(hwnd);
        hPen = CreatePen(PS_SOLID,5,RGB(0, 0, 255));
        SelectObject(hdc, hPen);

        int x = LOWORD(lParam);
        int y = HIWORD(lParam);

        MoveToEx(hdc,x,y,NULL);
        LineTo(hdc, LOWORD(lParam), HIWORD(lParam));
        ReleaseDC(hwnd,hdc);
    }
    else
        break;
}