你好

When meeting people for the first time, the most commonly used phrase is "你好！" Learn this and more greetings and farewells in this Google presentation.

If you have not learnt the vocabulary yet, check out the Quizlet Ni Hao 1 Lesson 2 here. In Quizlet first go to "Learn" and master the vocabulary, then try out the other activities. You can then test yourself to see if you have mastered the content when you are ready.