Instead of posting questions every time you don't understand something and hoping people will explain in the detail you want, start using Google to at least do some research for yourself.
I copied a bit of your question and pasted it into Google, and got over 57,000,000 hits - all of which look very relevant on the first page:
how does interpreter work - Google Search[
^]
Starting with Google means you get at least the basics much more quickly, as well as looking less of an idiot when someone looks at your question history ... and it means you don't waste the time of people who will just send you to the links Google would have found in the first place.
Give it a try: it's called "research" and it should be a valuable tool in the hands of every human being.