There is a manual on WEB TACHO: https://wiki.teltonika-gps.com/view/WEB_Tacho
To put it simply. FMB640 detects Ignition, once it is On every hour it connects to the Web tacho server to check if there are any schedules due to for download. If there are, appropriate company card that has that particular tachograph registered has to pass authorization on Our platform. If that company card is authorized to be used with that particular tachograph and there is a schedule that is due, download will be started.
If there are any specific questions please ask.