A lesson plan outlines what students will learn each day, including the content, teaching methods, and assessment. It is important for teachers to plan lessons because it helps them stay organized and focused on learning objectives. A lesson plan structure like the 4 A's model (Activity, Analysis, Abstraction, Application) guides teachers to engage students in the material through hands-on activities, analysis, reinforcing content, and applying what they've learned. Developing comprehensive lesson plans with clear objectives, materials, and assessments benefits both teachers and students by promoting an effective and structured learning process.