I am not sure how to display an image or text of my choice as a 2d overlay. For example, say your character finds a book somewhere and as soon he clicks on it an image or text shows up. I am not sure of the term used for this in Unreal Engine.
The documentation contains a lot of information and should be the first source of study, prior to looking at tutorials. If you scan or glance over all the Documentation then you’ll have a good idea of what’s available, later when you need to do a specific task you’ll have an idea of where to begin and tutorials can help at that point.
An alternative approach would be to create a custom HUD class which has it’s uses but UMG offers a more designer oriented approach.
I usually tend to use custom HUD classes if the overlay has complex logic behind it. On the other hand UMG offers a lot of standard input widgets which you would have program yourself when creating a custom HUD class.