I want to access a boolean variable from a widget blueprint and implement it into a level blueprint so a cutscene and some music will play when the play button is pressed at any time.
If you want to communicate with your level blueprint, you will have to use event dispatchers. This is because blueprints are not aware of the level blueprint. The level blueprint on the other hand, knows about other blueprints.
When you spawn your widget, make sure to save it in a variable. Inside the level blueprint, get the blueprint that contains your widget variable. Then setup your event dispatcher.
https://docs.unrealengine.com/latest/INT/Engine/Blueprints/UserGuide/EventDispatcher/index.html
How do i exactly set my widget blueprint to a variable?
In your first image, where you create the widget, right click the Return Value of Create Settings_C Widget and select Promote to Variable. It is possible the Set New Var node does not get properly connected, so just connect it. I suggest you rename the variable as well.
This variable can then be used to reference the widget in the future. An example would be when you want to Remove From Viewport or Remove From Parent to clear the widget from showing on the screen.
Note that removing the widget is not the same as destroying the widget from memory, so you can re-add the same variable to get the widget back. It will then be in the same state as the last time you saw it.
If you want to reset the widget, I suggest you either create a new widget from scratch or have a function for resetting all the objects inside the widget.
For our purpose, we want to use the variable to setup an event dispatcher. I recommend doing so from your Begin Play in the Level Blueprint.