On the home page, you will see displayed a list of all collections, the number of computers within each collection and the number of maintenance windows that exist for each collection.
The table is interactive, so if you drillthrough on a specific item, you will see its related page (List of Computers by Collection or List of Maintenance Windows by Collection). The footer on all of the pages tells you when the collection data was last refreshed (queried and imported into Power BI from SCCM).
Power BI, by default, displays all results. Once a filter is selected, for example, a Maintenance Window, it remains in place until replaced by another filter. Filters are generally enabled when you drillthrough from one page to another page.