in present simple tense, if the subject is 3rd person singular number then s/es is added with verb. but when is 's' added with verb and 'es' added with verb?

Add - s to the base form. This is the most common spelling for the -S form and is the spelling used for most verbs. Notice, especially, that - s is added when the base form ends in one or more consonants + e: aches, bakes, breathes, cares, caches, dives, types, writes Notice that - s is also added when the base form ends in one or more consonants (but without e): adds, bets, beats, calls, claps, cheats, cleans, digs, drops, eats, fills, finds, fits, gets, grabs, hops, kills, knits, links, lists, means, needs, opens, puts, quits, robs, rings, rips, sends, stops, tells, trusts, voids, wants, works, zips In addition, notice this spelling is used with the small number of verbs ending in two vowels (including - ie): agrees, argues, boos, coos, flees, glues, moos, sees, shoos, shoes, tees, woos dies, lies, ties, vies read less

Change y to i and add - es. This happens when a verb ends in a consonant + y: apply / applies; bury / buries; carry / carries; copy / copies; cry / cries; dry / dries; fly / flies; fry / fries; hurry / hurries; marry / marries; pity / pities; ply / plies; pry / pries; tidy / tidies; try / tries; worry / worries. Verbs that end in a vowel + y do not change the y to i and then add - es, however: buy / buys; employs / employs; enjoy / enjoys; flay / flays; lay / lays; pay / pays; play / plays; say / says; slay / slays; spray / sprays; stay / stays; sway / sways; Important: Compare flay / flays, play / plays, and pray / prays with fly / flies, ply / plies, and pry / pries to see how these spelling rules work for verbs ending in s. read less