You must specify the Super User token_auth as a parameter to this script, eg. &token_auth=XYZ if you wish to run this script through the browser.
However it is recommended to run it via cron in the command line, since it can take a long time to run.
In a shell, execute for example the following to trigger archiving on the local Piwik server:
$ /path/to/php /path/to/piwik/misc/cron/archive.php