We use the Present Perfect Tense to talk about experiences. Examples I have been abroad two times. Anna has never broken a leg. Have you ever eaten sushi? We often use 'never' and 'ever' with the Present Perfect Tense to talk about experience. We use the Present Perfect Tense to talk about an action which started in the past and continuous up to now. Examples I have been a teacher for more than ten years. We haven't seen Janine since Friday. How long have you been at this school? For more grammar tips, go to http://www.italki.com/knowledge/page/ENGLISH%20GRAMMAR.htm

In general, if we talk or write about the time or place of an event, we must use the Simple Past tense; we cannot use the Present Perfect Tense. Examples of Simple Past tense: I lived in that house when I was young. He didn't like the movie. What did you eat for dinner? John drove to Paris on Monday. Mary did not go to work yesterday. Did you play tennis last week? I was at work yesterday. We were not late for the train. Were you angry? Note that when we tell a story, we usually use the simple past tense

Present perfect is used to express/describe past events that have present consequences. "I have seen that movie." -->therefore I don't need/want to see it again "I have already eaten dinner." --> therefore I am not hungry. Also, unlike in the past simple tense, the time reference is not determined. "I have seen that movie, I just cannot remember when." "I saw that movie when it first came out as DVD."

I do want to make this clear: you can't substitute past simple for present perfect (I see many students who try). However, the criteria is pretty simple for deciding which to use. :) Are you talking about the past? Use past simple (ha! obviously). Are you talking about the present situation? Use present perfect. Present perfect uses a past event to describe, explain, or connect to the present situation. "I haven't eaten breakfast" explains why you are hungry now. "I didn't eat breakfast" tells me nothing about now. Perhaps you ate something a little later. When you use past simple, you are telling me that the event is done, finished and has no effect on the current situation. You also need to indicate when this past event happened. When you use present perfect, you are telling me that the past event has some effect on the present. You don't give a time of when the event happened, because that is irrelevant. The time you give is in the word "have": now.