Just add 's'

words that end in a hissing sound
add 'es'

words that end in
'f' or 'fe'

replace the 'f' or 'fe'
with 'ves'

words ending in
'consonant' + 'y'

= change 'y' to 'ies'

words ending in
'vowel' + 'y'

just add 's'

the word changes altogether

the word stays the same

words ending in 'o'

'latin' words
ending in
'us' = change to 'i'
'a' = change to 'ae'
'um' = change to 'a'
'is' = change to 'es'

exceptions