Rules for regular and irregular plurals of nouns

When you want to say the plural of a noun, in most cases all you have to do is add "s" at the end of the word, these are called regular plurals, for example: 

Hand _____ Hands

Number _____ Numbers

Book _____ Books

Plant _____ Plants

Program _____ Programs

File _____ Files

Boyfriend _____ Boyfriends

Ambassador _____ Ambassadors

Exchange _____ Exchanges

There are also some plurals where you add "es" at the end of the word. We do this when it ends in s, x, z, ch, o or sh, for example: 

Box _____ Boxes
Potato _____ Potatoes

Pitch _____ Pitches

Boss _____ Bosses
Volcano _____ Volcanoes

Bush _____ Bushes

Wish _____ Wishes

Buzz _____ Buzzes

Tax _____ Taxes
Hero _____ Heroes

Glass _____ Glasses 

However, we need to be careful, because some words ended in "o", when we write the plural, we just have to add "s", like: 

Disco _____ Discos

Photo _____ Photos

Piano _____ Pianos

There are nouns where the word ends in "consonant+y", in that case, you replace the "y" for "i" and add "es" at the end, for example:  

Fly _____ Flies

Spy _____ Spies

Penny _____ Pennies

Baby _____ Babies

Candy _____ Candies

Sty _____ Sties

When the noun ends in "f", we replace the "f" for a "v" and then add "es" at the end of the word, for example: 

Half _____ Halves

Wolf _____ Wolves

Loaf _____ Loaves

Shelf _____ Shelves

For the nouns ending in "ife", we replace the "f" for a "v" and add "s" at the end, for example: 

Wife _____ Wives

Life _____ Lives

Knife _____ Knives

When the noun ends in "us", whe cange it for an "i", for example: 

Cactus _____ Cacti

Focus _____ Foci

Nucleus _____ Nuclei

When the noun ends in "is", for the plural, we replace the "is" for "es", for example: 

Analysis _____ Analises

Crisis _____ Crises

Thesis _____ Theses

When the noun ends in "on", all we have to do is replace the "on" for an "a", some examples are: 

Phenomenon _____ Phenomena

Criterion _____ Criteria

There are special cases when the noun changes completely for his plural, like: 

Person _____ People

Foot _____ Feet

Mouse _____ Mice

Man _____ Men

Thoot _____ Theet

And for last, there are nouns that remains the same when we say or write their plural, for example: 

Salmon _____ Salmon

Sheep _____ Sheep

Deer _____ Deer

Fish _____ Fish

Tuna _____ Tuna