Its telling you that if you want certain kinds of energy to come to you, then be that kind of energy. I think the kinds of energy it's talking about is like 'positive' energy, energy here meaning whatever kind of attitude a person has, if that makes sense.

If you want people to be kind to you, be kind to them. Sort of like you get what you give.

in this context, energy refers to a person's character. For example, if the person has high and positive energy, it could mean that the person is a very energetic, bubbly, happy and kind person. If the person has low and negative energy, it could mean the person is constantly gloomy, pessimistic and discouraged. So the line is telling you that you should be positive and kind so that you also attract positive and kind people to be your friend.