'I want you to' is telling someone that you have a desire or would like for them to do something.  'I want you to' 是告诉别人你渴望或想要他们做某事。

Here are some examples: 这里有一些例子：

"I want you to clean the dishes." 

我想要你洗这些盘子。

"I want you to come home right after school." 

我想要你放学后就回家。

"I want you to call once you get there." 

我想要你一到那里就打电话。

"I want you to explain yourself to me." 

我想要你向我解释。

"I want you to educate me." 

我想要你教育我。

By using the word 'need' instead of 'want' you are expressing something that is required or wanted.  通过用'need'这个词来代替'want'，你是表达要求或想要某事。

Here are some examples: 这里有一些例子：

"I need you to study harder in school." 

我需要你在学校更努力的学习。

"I need you to stop and listen to me." 

我需要你停下来然后听我说。

"I need you to greet our guests." 

我需要你向我们的顾客问好。

"I need you to introduce me to your family." 

我需要你向你的家人介绍我。

"I need to request a refund." 

我需要退款。