We normally add -s to the verb with he, she and it.

When the verb ends in sh, ch, ss or x, add es:
✓ washes           ✗ washs
✓ watches          ✗ watchs
✓ kisses
✓ fixes
When the verb ends in consonant + y , change the y to i before you add es:
✓ fly – flies        ✗ flys