The verb to be is not used in Chinese the same way as it is in English. In Chinese, 是 (shì) is for connecting nouns, and is generally not used with adjectives.
The structure for connecting nouns with 是 (shì) is:
Noun 1 + 是 + Noun 2
This is equivalent to "Noun 1 is Noun 2" in English.
Chinese does not conjugate verbs. That is, the form of the verb is the same no matter who is doing it. In this case, it is always 是 (shì) and never changes. As you can see, it's easy to form simple sentences expressing to be in Chinese. The only tricky thing about 是 (shì) in Chinese is that it's used to link two nouns, so you can't rely too much on translating directly from English when it comes to expressing the English verb "to be" in Chinese.
- 我 是 学生。Wǒ shì xuésheng.I am a student.
- 你 是 John 吗？Nǐ shì John ma?Are you John?
- 他们 是 有钱 人。Tāmen shì yǒuqián rén.They are rich people.
- 你是 老板 吗？Nǐ shì lǎobǎn ma?Are you the boss?
- 这 是 我 男朋友。Zhè shì wǒ nánpéngyou.This is my boyfriend.
- 那 是 你们 公司 吗？Nà shì nǐmen gōngsī ma?Is that your company?
- 你 妈妈 是 老师 吗？Nǐ māma shì lǎoshī ma?Is your mother a teacher?
- 这 都 是 你 的 钱。Zhè dōu shì nǐ de qián.This is all your money.
- 那 是 什么 菜？Nà shì shénme cài?What food is that?
- 我 也 是 他 的 朋友。Wǒ yě shì tā de péngyou.I am also his friend.
Other Uses of 是 (shì)
Be careful and take note. As you can see above, 是 (shì) is only used to link two nouns. It cannot be used to link a noun and an adjective. This is a very common mistake for people just beginning to learn Chinese. For that kind of sentence, you'll want to use a different structure with the linking word 很 (hěn).
In Chinese it is also possible to use the phrase "是不是 (shì bu shì)?" It can be used at the beginning or end of a sentence. It's meaning is quite similar to the English expressions "right" and "aren't you?" This is very useful if you want to express concern for a person, or if you want to mix up your sentence structure a bit and make it more interesting. The 是不是 (shì bu shì) pattern is also part of affirmative-negative questions.
Another way to use 是 (shì) is to use it as a tag question. You can add “是吗?” (shì ma?) to the end of a question to mean the English equivalent of: "is it" or "yeah?" Using this in a question usually allows the speaker to get a confirmation answer.
- 他 没 听到，是 不 是 ？Tā méi tīngdào, shì bu shì?He didn't hear you, right?
- 你 是 不 是 还 没 吃饭？Nǐ shì bu shì hái méi chīfàn?Haven't you eaten yet?
- 你们 是 不 是 中 国 人？Nǐmen shì bu shì Zhōngguó rén?Are you Chinese?
- 你 到 了，是 吗 ？Nǐ dào le, shì ma?You have arrived, yeah?
- 你 有 两 个 孩子，是 吗 ？Nǐ yǒu liǎng gè háizi, shì ma?You have two kids, yeah?