singular and plural

(a) noun + -s : friends are important
     noun + -es : i like my classes

A final -s or -es is added to a noun to make a noun plural friend = a singular noun friends a plural noun


(b) verb + -s : john works at the bank
     verb + -es : she watches birds

A final -s or -es is added to a simple present verb when the subject is a singular noun or third person singular pronoun.
john works : singular the students work ; plural
he works : singular they work : plural


SPELLING : FINAL -s vs -es
(c) sing - sings
     song - songs

For most words (whel,then a verb or a noun ),simply a final -s is added to spell the word correctly.

(d) wash - washed
    watch - watched
    class - classes
    buzz - buzzes
    box - boxes

Final -es is added to words that end in, -sh, -ch, -s, -z,and -x

(e) toy - toys
     boy - boys

for word that  end in -yin (e) : if -y is preceded by a vowel ,only -s is added

(f) baby - babies
    cry - cries

in (f) : if -y is preceded by a consonant ,they -y is changed to -i and -es is added.