Agreement

The lion is hungry.

Ferry kicks the ball.

They swim in the morning.

In the three sentences, ‘lion’, ‘Ferry’ , and ‘they’ are called the subjects of the sentences.
They can be singular or plural.

“Lion’ and ‘Ferry’ are singular.
The verb ‘is’ and ‘kicks’ are also singular.
‘They’ is plural.
The verb ‘swim’ is also plural.

The use of singular or plural verb must agree with the noun it is used with in the sentence.
A singular verb must be used with a singular noun.
A plural verb must be used with a plural noun.

The verb is commonly learnt in its plural form – go, come, fly, wash.
To change them into the singular form, we can

add ‘s’

come – comes
run – runs

add ‘es’

go – goes
wash – washes

change ‘y’ to ‘ies’

fly – flies
dry – dries

different words

have – has
are – is