Earth's Axial Tilt
Earth's Axial Tilt is the lean of our planet that makes sunlight hit some places more directly than others.
Think of it this way
Hold a flashlight straight above a ball and the light hits the top in a tight, bright circle. Now tilt the ball to one side. The same beam spreads across a wider, dimmer patch on the tilted face. Earth stays tilted like that ball, so one half gets strong light while the other gets light spread thin.
Explaining earth's axial tilt by grade level
Earth does not stand straight up. It leans to one side. When your part of Earth leans toward the sun, light hits the ground more directly. That makes it feel warmer, and that is summer.