The phrase is structured as a verb-object compound: 节约 (jiéyuē), the action of “saving/economizing,” is applied to the object 用电 (yòngdiàn), the act of “using electricity.” Literally, it means “to be frugal with the use of electricity.”
The concept of 节约用电 is deeply embedded in Chinese culture and national policy. It's not just a suggestion; it's a widely promoted social norm.
You will encounter this phrase constantly in China in various contexts.