Sildes are content only modules. Decide what content you want to display. You can display multiple blocks of content on one slide.
In this resource:
To add a slide module, go to the project timeline and 'Add module', choose 'Slide', name it, and press 'Select'. The new module will appear in the module library.
You can also create a slide module by clicking on the plus sign in the timeline and choose a slide from the list. The module will in this case be placed on the timeline directly.
Click on your new slide module to edit it.
Drag and drop your slide module to the slot you want it in the timeline