Before you can push a vApp to the Catalog you have to fully power it off.

Click All Actions from the vApp view (three dots from the vApp list) then select the Create Template option.

Select the catalog you would like to deploy to. (Probably DefSec_Lessons)

Set name and description. If you are making a lesson please set the name to the meeting code from the schedule.

Make sure that you have the Customize VM settings option checked. Without this checked networking will be broken for all copies of this vApp.

Click OK and wait a few minutes for the template to be created.