Hello or Hi in Chinese is said 你(nǐ) 好(hǎo). You don’t have to worry about saying it wrong, most people will understand what you meant. It is always great to know a few words from a foreign language mostly if we have to visit that country, so you can put this one into your repertoire of how to say Hello in foreign languages. It is easy and simple.
You can use it to greet people, to start a conversation with friends or a complete stranger. As an example, before asking your way or any information to someone you don’t know, or to a working staff you can begin with 你(nǐ) 好(hǎo) and then ask what you want.

Other ways to greet in Chinese
您(nǐn) 好(hǎo): it is the polite form of saying Hello in Chinese. It is used to show respect, you can use it to greet high-ranking officials, teachers, customers, or people you care the most about.

Why you can use 您(nǐn) to address the people you care the most about?
The character 您 is formed of 你(nǐ) on top which means you and 心(xīn) on the bottom which means heart. This is the kind of characters that make Chinese very straightforward and will make you love studying the Chinese language. In many languages like English, words are just words and we have to memorize them to understand their meaning, but some Chinese characters speak by themselves. You see them and you say to yourself, that really makes sense. However, I also have to agree, that many of them are also very similar.

哈(hā)喽(lóu): this is Hello in Chinese. It’s much easier than to say 你(nǐ) 好(hǎo). You can use it to greet your friends and people you are very familiar with.
嗨(hāi): This is Hi in Chinese. The Chinese language is very rich and diversified. You can see that, you don’t need to know Chinese to say Hello, you can just say Hi and you are already speaking Chinese. When you see from this way, Chinese is not that hard, right?

午(wǔ)安(ān),: That means good afternoon.

下(xià)午(wǔ)好(hǎo): also means good afternoon.
晚(wǎn)上(shàng)好(hǎo) : Means good evening.

Festival greetings

During festivals, you can use the festival name and mostly the character 好(hǎo) to greet people.
新(xīn)年(nián)好(hǎo): greeting for the Chinese new year.
过(guò)年(nián)好(hǎo): is also a greeting for the Chinese new year.

Relatives greetings

To show respect, when you see your relatives, you have to greet them or greet them back if they greet you first. In Chinese, you can do that by saying the relative title and adding 好(hǎo). You should not ignore people in China, especially relatives as you may make them lose face, and face is a very important thing in China.
叔(shū)叔(shu)好(hǎo): Generally speaking, this is the greeting for dad’s younger brother. But you can use it to greet your father-in-law when you’re not married to his daughter yet.
阿(ā)姨(yí)好(hǎo): This is a greeting for your mom’s sisters, but you can also use this to greet your mother-in-law before getting married and you can also use it to address any woman of the same age as your mother.
You can use the same structure to greet other relatives as grandfathers(爷爷(yéye), 外公(wàigōng)), grandmothers (奶奶(nǎinai), 外婆(wàipó)) and other relatives you may encounter.

Public greetings

大家好(dà jiā hǎo): you can use this greeting to greet a large crowd of people at the beginning of a public speech of any kind.
你们好(nǐmen hǎo): You can use this one to greet a group of few people.