How to make canvas and text on it invisible on another levels? My text from main level shows on the start menu level. How to make it work only on main level?
Hey @Yxochka! Welcome to the forums!
When you leave the “MainMenu” level, before the loading of the next, you need to grab that widget and “Remove From Parent” and it will get rid of it as part of your moving to the next level. 
If you need to get it back just use “CreateWidget” and put in the class!
This text should be in the main level only. But when I start game with level start menu it shows too. In the level start menu blueprint “event begin play” already with menu widget. Please, can you explain more.
You need to look at where the widget is being created. If it is created on something used in every level, it will appear in EVERY level. I cannot advise you much further without more info- screenshots would help quite a bit! Screenshot of the code where you put this main menu widget.