Hi = 嗨 = hai
Hello=你好= Nihao
How Are you? = 你怎么样？= Ni zenmeyang?
where you from? = 你来自哪里？ni lai zi na li?
how old are you? = 你几岁？ 或者 你多大了？ 或者 你多少岁？= Ni ji sui(i.e for little kids) or Ni duo da le(i.e for teenager's and above).

nice to meet you = 认识你很高兴 = ren shi ni hen gao xing。
welcome = 欢迎= huanying
thank you= 谢谢你= xie xie ni。

Hope it will help you.

Hi   嗨  Hai
where you from? 你来自哪里  Ni Lai Zi Na Li
how old are you? 你几岁  Ni Ji Sui

nice to meet you很高兴认识你 Hen Gao Xing Ren Shi Ni
welcome欢迎 Huan Ying

How can you discuss the words with proper pronunciation when you are writing them? If you look up the character and cut and paste it into Forvo.com you will hear the pronunciation. 

You can find all of these phrases online in seconds, in fact, just spend a few minutes looking round this site and you will find your answers! 

I just know that hello is <em>ni hao</em>.