This functionality allows you to systematize your designs throughout your application. In Figma these are called "components", in Sketch or Adobe XD they are referred to as "symbols".
To create a reusable component in Uiflow, select the element that you want to repeat throughout your project, open the element menu, and select "Create Reusable." Alternately, you can use the keyboard shortcut Option Command K.
The new component will appear at the top of your element catalog in a section called Reusable Components:
To detach the instance, you can either go back to the element menu and select "Detach Reusable" or use the shortcut Command Shift B.