Here you go.. Is used when someone is giving you something, usually informally. Like a waiter at restaurant serves you the dish and says " here you go " There you go. Multiple meanings. Can be used like here you go, except something away from you, like " over there". It is also used in a way to say, yes you got it. If you are practicing saying something, or a sport and you get it right, your coach may say " there you go ". Like yes you got it right !. Here we go .. This is used as you say, it usually is used as lets go, or we are going. Like driving a car and you all in the car and the driver says, " here we go " .

To me you are asking on verb tenses and use. I thought this might help you. http://www.englishlanguageterminology.org/parts-of-speech/verb-tense-chart.htm Here you go I might use if I am giving something to someone else maybe now, There you go is the you gave the book to another or similar object. Here we go yes is like saying let's go.