How to create a UML diagram quickly in Modelio?
You just need some clicks to create a diagram. Of course this technique is available for other type of diagrams (BPMN, ...).
Select a UML element, right-click and select "create diagram...".
Please note that this video does not contain sound.

Demo performed with Modelio 3.7. This technique should be applicable to Modelio 3.* versions.