Learning Chinese language well is not so easy for most of foreigners. However, we can learn it starts from some usefull and common sentences.
Chinese does not have words for "yes" and "no" as such; instead, questions are typically answered by repeating the verb. Common ones include:
 

When someone ask, are you American?

Nǐ shǐměi guárén mǎ?

Answer: Yes/No
是shì/不是bú shì

Somone ask, Do you have a pen?

Nǐ yǎu bǐ mǎ?

Answer: Yes, I have/ No, I do not have
有yǒu/没有méi yǒu

When you meet someone, you can say

Hello.
你好。Nǐ hǎo.

How are you?
你好吗？Nǐ hǎo ma?

When someone say 你好to you, you can say

Fine, thank you.
很好, 谢谢。Hěn hǎo, xiè xie.

When you are interested in someone, want to know his/ her name
May I please ask, what is your name?
请问你叫什么名? Qǐng wèn nǐ jiào shěn me míng?

Who are you?
你叫什么名字？Nǐ jiào shén me míng zi? (Not so polite than the las sentence)

When you are asked the name

My name is John .
我叫 John 。Wǒ jiào John .
Nice to meet you.
很高兴认识你。Hěn gāo xìng rèn shì nǐ.

Want to be polite and gentleman? You must remember these words below

Please.
请。Qǐng.

Thank you.
谢谢。Xiè xiè.

You're welcome.
不客气。Bú kèqi.

Excuse me. (getting attention)
请问qǐng wèn

Excuse me. (begging pardon)
打扰一下。Dǎ rǎo yi xià

I'm sorry.
对不起。Duì bù qǐ.

It's okay. (polite response to "I'm sorry")
没关系(méiguānxi).

Good morning.
早上好。Zǎo shang hao.

Good evening.
晚上好。Wǎn shàng hǎo.

Good night.
晚安。Wǎn'ān.

Goodbye
再见。Zàijiàn

Goodbye (informal)
拜拜。Bai-bai (Byebye)

Still fill poor in Chinese?

Don’t worry, there must be someone can speak English

I can't speak Chinese.
我不会说中文。 Wǒ bú huì shuō zhōngwén.

Do you speak English?
你会说英语吗？Nǐ huì shuō Yīngyǔ ma?

Is there someone here who speaks English?
这里有人会说英语吗？Zhèlĭyǒu rén hùi shuōYīngyǔma?

I don’t understand.
我听不懂。Wǒ tīng bù dǒng.

Looking for toilet?

Where is the toilet?
厕所在哪里？Cèsuǒ zài nǎli?

When you are in emergencies
Help! (in emergencies)
救命！Jiùmìng!