Everything in Beautiful.AI gets created in the container of a 'presentation'. By default, a Title slide is the first slide, but you can just delete it after you create a second slide.
To create a slide, click on New Presentation:
On the right-hand side of the slide, click the Add Slide icon to add a slide:
The Templates library will launch. Select the template you want from the menu or type in the name or item in the search bar. The slide will automatically launch once selected: