The urgency of sustainability concerns has intensified in recent years, sounding alarm bells over the planet's condition and prompting nearly every industry and practice to reassess their contributions to the climate crisis. Software engineering is not immune to this scrutiny. Software engineering practices significantly affect the environment and may not align with sustainability goals. Although sustainability is a relatively recent focus in software engineering, it has garnered increased attention, with numerous studies addressing various concerns and practices. Green software engineering aspires to develop dependable, enduring, and sustainable software that fulfills user requirements while minimizing environmental impacts. As this green paradigm gains traction in software engineering, practitioners must incorporate sustainability considerations into future software designs. However, despite the surge in green software engineering research, a universally accepted definition and framework remain elusive. This paper outlines green software engineering by explaining its principles, challenges, and methods for measuring and evaluating software effectiveness in this context.