There are some occasions where you have to use some rules.
Spelling rules for He/She/It:
Normally most verbs add -s: I walk -> he walks
Verbs ending with sh,ss,o,ch,x add –es:
I wash -> He washes/ I stress-> She stresses/ I watch -> It watches
I go -> He goes / I relax -> She relaxes
Verbs ending in consonant + y changes to –ies: I study -> She studies
Irregular verbs like have -> has