Both are used to indicate you are talking to another person. So you can say kifak inta? Meaning how are you? Or you can just say kifak and drop the inta. Both are correct. Often arabic speakers will drop the inta in favor of having the conjugation attached to the verb or noun so pay attention to conjugations if inta (or inti) isnt present

inta and hadretk means you , but hadretk is a legal word used to show the respect

hadretak means " your presence" and it's like "your majesty" and "your highness", we use Hadretak when we speak to Old people, parents or a teacher to show respect. I hope this answers your question.