Remember a cause is something that happens, and an effect is something that changes because of it. Example:
Cause: George was sick
Effect: He couldn't come to the sleepover
Birds migrate south because food supplies become scarce and the cold winters make survival harder, so they migrate closer to the equator, where temperatures are warmer.
Cause: Winter arrives, making survival difficult
Effect: The birds move south for the winter season
Remember: The cause is an event that happens, and an effect is something else that happens because of it.