I have read about how your body adapts to workouts based on the energy system that you work in. What are the different energy systems, and how would you target them?

I believe you're talking about aerobic and anaerobic. You would target them by doing things that tap into that. Aerobic means your body uses fat and glucose for energy and oxygen is present. Anaerobic means oxygen isn't as much of a factor and glucose is the preferred energy source (not accounting for post exercise burn, which is another story). So aerobic is something like jogging, anaerobic is lifting weights for lower rep ranges like 3-6 rep training