Jquery how to use ajax?

Jquery how to use ajax?

Hi, I am using ajax via jquery. I  have a huge problem. I  need to send some text to my php file.  My php file will return a response in json. 

I have set datatype to be json. However, my text doesn't get to my php file.  It will only send my text data to the php file only if I don't include the datatype of json.  

The problem is that I need to send text data to my php file but receive json data. Since  I will receive arrays. 

How can I do this? can  is there a return datatype option? So I can only specify the return data type?