How to USE a date table

I'm not understanding why this is so complex for me to comprehend!! Please stay with me here... :)

Trying to be more open minded.

I tried two things:

ONE:

1a. I imported a date table, and I defined that as "the one and only date table" that a model can have.

1b. This did nothing automatically. This added no hierarchies to all of my dates on the fact tables.

1c. I published the report to PowerBI Service. There were no automatic drill or filtering capabilities on Month/Quarter/Year (all attributes on the date table).

TWO:

2a. Manually defined a date table like you describe using DAX. I then flagged this as "the one and only date table" that a model can have.

2b. This did nothing automatically. This added no hierarchies to my dates from the fact tables.

2c. I published the report to PowerBI Service. There were no automatic drill or filtering capabilities on Month/Quarter/Year (all attributes on the date table).

Thus... I still persist declaring a table as "the one and only date table that a model can have" as practically useless? I am not understanding what features this enables by "declaring" that table as "THE DATE TABLE".

I hope you make sense of my confusion and can point me to a how-to video, etc for the purpose of declaring a date table. Thank you Nolock