Archiving is maybe a bit of a misnomer.
When people visit your website, their raw visit data (what happened) is stored in the visitor log. But to create all other reports, Matomo has to do more complex aggregation of all data. This is called archiving.
Normally this happens whenever you view a report. But the more data you have, the longer it takes. So if you have now setup auto-archiving, Matomo will create the reports on a regular basis. This has the huge advantage that whenever you open Matomo, the reports will already be available and Matomo feels much faster (as it just has to display them).
If you want to check if the archiving is working correctly, you can check the output of the task (I have no idea where you could find it on Windows)