https://URL_TO_PostAffiliatePro/scripts/click.php?a_aid=refid&a_bid=73d672s1
The click.php script creates a browser cookie in visitor's browser, registers a click to an affiliate with the particular refid and registers a per click commission (if defined) computed based on the campaign to which the banner identified by a_bid variable belongs. When the click is saved and browser cookie created the visitor is redirected to the Destination URL defined for this link, e.g. https://mywebsite.com/. So when you click on a link like
you will immediately get redirected to the Destination URL (target URL) defined in the banner with ID represented by the value of a_bid in the link you have clicked - https://mywebsite.com/.
If you should want to disable the creation of cookies you can add to the redirect link &mode=SC parameter thanks to which the cookie will not be created on the Post Affiliate Pro domain. This can be useful if you cannot create cookies due to legal reasons or you don't need them for tracking. The redirect links can pass the tracking ID to the destination page in a visitorId parameter which can be saved on the server side. To enable passing of this parameter in all redirect links automatically go to your merchant panel and to Configuration->Tracking settings and check the checkbox called Add visitor id to redirect urls towards the bottom of the page.
If you don't mind having the cookies created and you just want to have higher tracking accuracy you can include the visitorId parameter and use the javascript click tracking code on the landing page which will automatically read this parameter and set the first party and flash cookies accordingly.