When something surges, it rises or increases a lot or moves forward very quickly, in a big, grand way that reminds you of an ocean wave. And, a surge of something is a strong, sudden increase of it.
Often, it's water that surges. This water is surging downhill.
But anything that moves in a big mass like a wave of water can surge. Often, we talk about crowds of people surging, or surging forward, or surging through a place. In the gif below, people are surging through the streets. And as you can see, surging is movement that's fast and sudden.
You might feel a surge of energy: a big, sudden wave of energy. Or a surge of happiness: a large rush of happiness. Or a surge of excitement: a new burst of excitement. In fact, if any feeling hits you like an ocean wave, you can call it a surge.