的 [de] is such a widely used auxiliary word. It appears everywhere in Chinese news articles, as well as in daily speech. Here are the rules for the most common uses of 的:

1. Possession
的 indicates possession.
For example:
我的（my）, 他的（his）, 她的（her）, 他们的（their）, 学校的（the school’s), 公司的（the company’s）

2. Creating nouns and noun phrases
的 can be attached to a variety of words or phrases, and the result will function as a noun, or a noun phrase.
For example:
这是我的。(attached to a pronoun)
This is mine.
我要红色的。(attached to an adjective)
I want the red one.
这台电脑是学校的。(attached to a noun)
This computer is the school’s.
今天来参加派对的都是美国人。(attached to a verb-object phrase)
The people who attended the party today were all Americans.
我说的是真的。(attached to the verb 说)
What I said is true.

3. Emphasis
是…..的 is a sentence structure which is used to express emphasis.
Examples for affirmative patterns:
我是昨天到上海的。（Emphasizing the time）
It was yesterday when I arrived in Shanghai.
我是坐地铁来公司的。（Emphasizing the way or manner）
It was by subway that I traveled to the company.
我和他是在酒吧上认识的。（Emphasizing the place）
It was in the bar that I met him.
是王先生开车送我回家的。（Emphasizing the person）
It was Mr. Wang who drove me home.

4. Asserting an affirmative tone
Putting 的 at the end of a statement can strengthen the affirmative tone.
Examples:
我知道这事儿的！
I know this!
你的梦想会实现的！
Your dream will come true!
别担心，他会好的。
No worries, he’s going be fine.

5. 什么的
什么的 is a fixed structure, placed after juxtaposed words or phrases, which means the same as ‘and so on’ or ‘etc’ in English.
For example:
她喜欢猫、狗、猪什么的。
She likes cats, dogs, pigs, and so on.
我们谈了电影，小说，音乐什么的。
We talked about movies, novels, music and so on.
周末，我喜欢看电视、上网、购物什么的。
During the weekend, I like watching TV, surfing the Internet, shopping etc.

(Source: italki.com)