You can add agenda items to your meeting on the Meetings & Offline tab.
Click the Agenda tab under your meeting:
Next you'll click + New Agenda Item:
The Meeting Agenda Item window will pop up, allowing you to enter a Title, Description, and optional Start time (if applicable.)
You also have the option to allow participants to register to speak on a specific agenda item:
Once you've added your agenda items, you'll see them under the Agenda tab for the associated meeting:
You can grab the three lines to the right of an agenda item to drag & drop to rearrange the order.
You can also edit the agenda item by clicking the edit (pencil) icon, or remove the agenda item by clicking "Remove from set," which appears on hover.
Check out the other meeting tabs: