ref – https://www.learnenglishlanguagewell.com/grammar/verbs-with-s-in-present-simple/

In English, the -s is only added to regular verbs in the present tense when the subject of the verb is a third person singular subject.

Let’s look at some simple examples:

• I run

(first person)

• You run

(second person)

• He/she/it runs

(third singular)

• We run

(first plural)

• You run

(second singular)

• They run

(third plural)

We add “s” to the end of a verb (run –> runs, sit –> sits, see –> sees, play –> plays)

We add “es” to the end of the verb that has a sibilant sound. i.e ss, ch, x, tch, sh, zz

example:

guess > guesses
watch –> watches
mix -> mixes)
smash –> smashes
buzz –> buzzes

Plural pronoun

This -s is different from the plural -s. Do not confuse the two.
i.e The subject “Lisa and Ronald” is a third person plural subject, so the verb DOES NOT get an -s.

drop singular plural
first person → I drop the ball. We drop the ball.
second person → You drop the ball. You (all) drop the ball.
third person → He/She/It drops the ball They drop the ball.

Notice that the verb is always drop in the present tense, unless the subject is third person singular.
Subjects like “Lisa and Ronald” are third person plural subjects. The names can be replaced by the third person plural pronoun “they” in the sentence, as shown below:

Lisa and Ronald drop the ball. = They drop the ball.

Other rules