The PRESENT PERFECT TENSE is formed with a present tense form of "to have" plus the past participle of the verb (which can be either regular or irregular in form). This tense indicates either that an action was completed (finished or "perfected") at some point in the past or that the action extends to the present:
I have walked two miles already [but I'm still walking].
I have run the Boston Marathon [but that was some time ago].
The critics have praised the film Saving Private Ryan since it came out [and they continue to do so].