The dative case expresses the idea of addressee. In English, it is used the preposition "to" for expressing this idea.

Я дал это тебе. - I gave it to you.

See the table with endings of nouns in cases here.

In Russian, we also use the dative case whenever we talk about age. So basically we say "it is 33 years to me" (мне 33 года).

The word “years” changes depending on the number of years. After five, age is measured in “summers”.

• 1 год
• 2, 3, 4 года
• 5 – 20 лет

Note that after twenty the form of the word "years" (год, года, лет) depends on the last number.

• Мне 21 год (I'm 21 years old)
• Тебе 24 года (You are 24 years old)
• Ей 25 лет (She is 25 years old)

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If you need to name a person, you should use the dative case for nouns:

• Это Марк. Марку 40 лет.
• Это Елена. Елене 51 год.

And by the way, we don't change names ending in -o (Диего, Матео, Педро) in cases, and we don't change females' names which do not end with -а or -я (Меган, Кейт). But males' names which end with -а or -я are changed like feminine nouns (you remember that Russian nouns ending in -a or -я are feminine gender nouns).

The same rule applies whenever we want to say if we like something or need something.

Мне нравится. - I like it (It is pleasing to me)
Марку нравится работать - Mark likes working
Мне нужно. - I need it (It is necessary to me).
Елене нужно работать - Elena needs to work.