Once you have created and laid out your Widget Blueprint, in order for it to be displayed in-game, you will need call it by using the Create Widget and Add to Viewport nodes inside another Blueprint (Level Blueprint or a Character Blueprint for example).
In the example above, the Create Widget node is calling the Widget Blueprint specified under the Class section (Owning Player is the Player Controller it is applied to where blank results in the default Player Controller) and the Return Value is the resulting product.
Also in the example above, the Return Value is being assigned to a variable titled Main Menu which allows us to access the Widget Blueprint later instead of re-creating the Widget (and this can be used to remove the Widget). Finally, the Add to Viewport is what draws the Widget Blueprint onscreen and we are specifying that the Main Menu variable (which holds the created Widget) be the Target that is added.
To remove the Widget from being displayed by using the Remove from Parent node and specify the Target Widget Blueprint.