You screen shot show FB live producer on Use Camera. That is something you'd do if NOT using OBS (where you'd be using the stream key instead)
I recommend reading Facebook's guide to settings (though OBS auto config setup for FB should cover the basics)
Then read either Facebook's or some other basic guides to using FB's Live Producer with OBS. I'd recommend avoid the gamer oriented guides (though some may be excellent, many are not, and being non-technical, may just confuse things for you)
Oh, and read the basic requirements for both live streaming and OBS. Windows 8.1 is very old and not supported, and shouldn't be used, for the most part, in a networked setting, especially not something connected to and using the Internet. Win10 is a free upgrade. If your PC is tool old, or ARM (vs x86 based) and can't be upgraded, expect issues with highly demanding compute task of real-time video encoding
