I wish I would understand even a fraction of the stuff that's going on with software synths. Every couple of years I get this fancy idea of "I'd really like to create some sounds/music", which usually ends up with me aimlessly manipulating digital knobs and switches on some massive UI, creating weird sounds with no real structure and changing all the default settings. The other option being something like FruityLoops…
Here's a rough crash course from someone who also struggled to get started:
1: You start out with a wave (sine, saw, pulse, etc). No synth starts out with a pure form of these waves. They all add a little color. Most synths have 2-5 oscillators (they produce the waves), often with each having different controls.
2: The filter constrains the sound. So, for example, if you wanted to make a bassy instrument, you'd filter out most of the high frequencies. The Attack, Sustain, Delay, and Release settings affect length and volume over time. This is what you use to turn waves into plucks, kicks, claps, strings, and anything else you can think of.
3: Most synths have at least 2 LFOs, or low frequency oscillators. You can connect these to different controls across the synth and change the timbre in weird, sometimes unpredictable and amazing ways. With Helm in particular, you click the little helmet by the LFO and drag the little bars on the different controls to change how much the LFO affects it. You'll see a little green bar pop out and move with the LFO. Serum has a separate tab with LFOs and routing to synth controls.