Not many instructors talk aobut raising your energy in riding. But, since we want to ride with the least amount of cue necessary to get the desired result, that comes down to energy. It's the most subtle cue of all.
If you don't care to ride from such extremely subtle cues, then you can go up to more obvious ones, like seat, and like leg, and then spur or crop. But, the horseman/woman should always seek to refine the communication with the horse, so that as little as possible is needed. This makes it possible to get a really big reaction if needed, when you DO go to the bigger cues (spurs, crop, etc).
If you are new to riding, it is going to be hard to know how to do such subtle cueing. 99% of riders just skip right over the "raise your energy" and go straight to the leg/spur/crop. I know that I am "guilty" of that all the time.