Three types of actions can be added to a page – launch an activity, launch a live question, and open a link :

1 - Access to your Presentation

Go on the Step 4 of your Session "Presentation", then click on "Create a Presentation".
You'll be able to either import an existing presentation, either to create a new one, from scratch.

To add an action to the page, simply use the in the top right of each page

2 - Choose the action you want to add

To find out more about creating and running your own activities, take a look at the resources available at this link.