The basic rules of forming plural nouns

Hello, dear student!
Today I would like to talk about the nouns which are transformed in the transition to plural form.

Nouns which are transformed in the root

Masculine nouns:
Singular - Человек [Chilavek] A person

transforms into
Plural - Люди [Lyudi] People

Let's look at other examples of the transition of masculine singular nouns to plural ones:
Сын [Syn] A son - Сыновья [Synav'ya] Sons (Plural)
Друг [Druk] A friend - Друзья [ Druz'ya] Friends (Plural)
Стул [Stul] A chair - Стулья [Stul'ya] Chairs (Plural)
Ребёнок [Ribyonak] A child - Дети [Dehti] Children (Plural)

Feminine nouns:
Дочь [Doch'] A daughter - Дочери [Docheri] Daughters (Plural)
Мать [Mat'] A mother - Матери [Matiri] Mothers (Plural)

Neuter nouns:
Яблоко [Yablaka] An apple - Яблоки [Yablaki] Apples (Plural)
Время [Vremya] A time - Времена [Vremina] Times (Plural)

Masculine nouns which have stress on the flexion –А/Я in nominative case, plural:
Цвет [Tsvet] A colour - Цвета [Tsvita] Colours (Plural)
Поезд [Poezd] A train - Поезда [Paezda] Trains (Plural)
Учитель [Uchitil] A teacher - Учителя [Uchitilya] Teachers (Plural)

Nouns which keep the same form (q.v. an article about the nouns which have only singular or plural form)
Borrowed nouns or nouns which have foreign stem never modify their form:
Радио [Radio] Radio - Радио [Radio] Radios (Plural)
Метро [Mitro] Metro - Метро [Mitro] Metros (Plural)
Меню [Minyu] Menu - Меню [Minyu] Menus (Plural)
Пальто[Pal'to] Coat - Пальто[Pal'to] Coats (Plural)