How can i use ui button clicked event at level blueprint?
You can’t. The “On Clicked” event is for a specific UI button not for a level BP. What are you trying to do exactly?
I made a “START” button and i want to start play when it’s clicked
Sounds like you just need to use the node “Open Level” and type in the level name of your first level. So the logic is like this:
On Clicked (Start Button) → Open Level