Social Media Marketing Podcast -- I don't get it sometimes

The Social Media Marketing Podcast sometimes makes me scratch my head and ask, "Huh?" I understand what social media is: Twitter is 140 characters that are shared with people who want to read our tweets. I think hashtags (#) are tags that are searchable. I understand Facebook completely. What I don't understand is a)how those tweets and posts can be monetized; b)why Pepsi or some other company would pay big bucks for posts and tweets when you have to have thousands of listeners before they sponsor your podcast. I did understand an episode that was devoted to podcasts. But most of the conversations are way beyond me. That might mean I'm too old for this social media marketing or it might mean the show assumes the audience is a lot more sophisticated about social media marketing than we really are. I'm assuming a combination is closest to the truth.