Instant Agenda meetings are fully reusable. After you end a meeting, you can restart it at any time. For example, if you run a weekly staff meeting, you can use the same URL to link to the same meeting each week. Every time you click Start Meeting, a new instance of the meeting begins.
Any topics not discussed or deferred in a meeting session will remain on the agenda for a future session. It helps to think of the agenda as a queue of topics that you can fill up over and over.
You can also see topics covered in previous instances of the meeting in the History tab. There is a summary for each session of the meeting that you have run.
If you have a recurring topic that you cover every week, you can edit the topic and check "Recurring Topic". That topic will re-appear in your agenda every week.