Nouns ending in "y" can be made plural in two different ways depending on whether there is a consonant or vowel before the y. If there is a consonant before the y, add "es" to form the plural (e.g. baby becomes babies). If there is a vowel before the y, simply add an "s" to form the plural (e.g. toy becomes toys). The document provides examples of common nouns ending in y and their plural forms to illustrate this grammar rule for forming plurals of nouns ending in y in English.