Okay, I can find a signal on the waterfall plot. Now what?

Got my first SDR yesterday, a NESDR SMArt with the starter set of antennae. I'm using CubicSDR on Mac. I can tune in to FM and AM radio stations without much of a problem, but haven't had any luck with anything else. Last night I had a Baofeng tuned to 147.125khz and was able to listen in on some radio conversation between some HAM operators (can't transmit, don't have a license yet), but I couldn't get my SDR to pickup the voices.

Anyway, surfing through the different bands I can adjust my plot, gain, and antenna to identify hundreds of clear lines of signal along all different parts of the radio spectrum. Sometimes I can get a sound that seems recognizable as some sort of data transmission, but usually it sounds more like noise.

Sooo, now what? Where do I go from here?