Possible Duplicate:
How do the tenses in English correspond temporally to one another?
When is the present perfect tense used instead of the past tense?
When will “Present Perfect vs. Past Tense” cases be affected by culture?
I'm having hard time to understand when do we use "They've insist" and "They insisted". As I'm aware of, you can't say "They've insisted".
For example, I would like to say, "They have insist to take a picture with me" sound same as "They insisted to take a picture with me". On which situations I should use one of this sentences?
This is probably very often question asked here but nobody can't tell me straightforward answer.