In this video, the teacher explains how to form irregular plural nouns that drop the Y and add ies. They emphasize the importance of checking if the word looks right in the sentence to determine the correct spelling. The teacher provides examples such as "pennies" and "butterflies" to illustrate the rule of dropping the Y and adding ies when a singular noun ends in a consonant and Y. They also mention the rule of simply adding an S when a singular noun ends in a vowel and AY. Overall, this lesson helps students understand and apply the correct spelling of irregular plural nouns.