Rules of putting s/es for verbs

In a simple present sentence where he, she, it or a name is the subject, verbs can end in -s or -es depending on the way the verb ends.

1. For most words, just add -s to the end of the verb.

Verb Ending	+ s	Examples
One or more consonants	+ s	calls sends wants
One or more consonants + e	+ s	likes races writes
-ie	+ s	lies dies ties

For some verbs, however, we need to add -es to the end of the verb.

Verb Ending	+ es	Examples
-o	+ es	goes does soloes
-sh, -ch, -tch -x, -z, -ss	+ es	kisses watches buzzes fixes splashes
consonant + y	Change the -y to -ie and add s	dries flies worries

Also,  pronunciation of different forms is different for -s and -es. Depending on the base verb, the ending can be pronounced as 's', 'z' or 'iz'.

Verb Ending	Pronunciation	Examples
Most consonant and vowel sounds	z	goes runs
p, t, k, or f sounds	s	Cooks Likes laughs
s, z, ch, sh or x sounds	iz	Notices touches

Courtesy : http://www.eslcafe.com/