How do I look at past or future priorities?

The main Priorities page is split into 4 sections:

Daily
Weekly
Monthly
Quarterly

You can scroll from left to right on each section where you will see:

< Yesterday or Tomorrow >
< Last Week or Next Week >
< Last Month or Next Month>
< Last Quarter or Next Quarter>

You can also use the date selector at the bottom of the page to view priorities for any date in the past.

Additionally, you can click on "See my uncompleted priorities" at the bottom of the page and see all Priorities not marked as Complete. This is useful to make sure you haven't missed something important.