Flag module views integration
If you want to display a list of content a user has flagged - You want build your view as you would any other. Then you add a relationship to the view for the flag you wish to display. 

If you wish to allow your user to simply add a flag directly from the view results, you would add a field to the view of the type "Flags: Flag Link". This will add the add/remove flag link to each result in your view.