now I can make it work with user-profile.tpl.php page,all this page does is to use
//print render($user_profile);
but this template page is kind of simple for me, because I want to add more content to show, I want to show some content beyond the user profile, like some content I had flagged with flag module, or some comment I made on the content, how should I extend this user-profile.tpl.php,
or should I not use this but use a view instead?
It would really be best to use a view for this. What I would tend to use any .tpl.php files for would be for creating css classes around elements, or if for some reason you need to do something involving an if statement or a loop when doing something to the HTML of the user page. However to simply display lists of things would be best done using the views module, and displaying it on the page with a block.