你好【nǐ hǎo】

你好 is the all-purpose greeting. It works at any hour, with anyone, and it needs no reply beyond 你好 back.

您好 is the polite form, for a teacher, a customer or anyone older. 大家好 addresses a group.

Greetings by time of day

早上好 in the morning, 晚上好 in the evening. 早 alone is the quick version between people who know each other.

你好吗 is not "how are you"

It looks like the English question but it is not used the same way. Between people who see each other often it sounds like a textbook. What a Chinese speaker actually asks is 吃了吗, 忙吗, or 最近怎么样.

你好吗 is fine after a long gap, or when genuinely asking about someone's health.

Leaving

再见 is the standard goodbye. 明天见, 下次见 and 一会儿见 all follow the same shape – time word plus 见.

Thanks and apologies

谢谢 takes 不客气 or 不用谢 in reply. 对不起 takes 没关系.