In Elements, diagramming is by default 'hierarchical', meaning that for any created diagram, you can select any of its boxes and create a 'child' diagram from that box. There is no limit to how many diagrams can exist in a hierarchy.
The entire hierarchy of diagrams is what we call a 'map'. When you create a new map, by default you create a single 'top' level diagram. That diagram inherits the name and description from the 'map'.
If you want to have many separate, stand-alone diagrams, you need to create separate maps.
Create new map
In the main Elements Home app, select "Diagrams" from the left-hand menu
Click on the NEW MAP button to create a new map. You will have an option to choose different types.