Hokay ~ just starting out on my second season of road riding, 2.5 years of spinning classes, bla bla bla

How do I know I'm sitting correctly in the saddle? I hear the phrase 'sit bones' all the time, but I'm not sure if/when I'm doing it right?! Is there a diagram for this stuff? I do get sore down under, shift around a bit till I find a comfortable position, for as long as that lasts - sometimes it works and sometimes it doesn't ... just feeling like I don't know what I should be aiming for?

thanks!