Reiki is usually described as an energy healing system.
I started giving treatments right after completing the first level training. Like any other practitioner, at first I treated only friends and family. Some of them were sceptical, they wanted to know more about this strange energy. After all, terms like spiritual energy or universal energy are quite abstract.
Being sceptical is good, so long as your scepticism doesn't prevent you to try and experience something for yourself. So, instead of giving them an explanation, I just offered a treatment. After that, no further explanation was necessary, and they wanted more!
Being able to help and heal other people was the reason I got into it in the first place, but its extent doesn't have to end there. Reiki is also a spiritual path. There's so much richness in it!