Starting game issue

Hey there , well I'm new in Unity and my problem might be really simple but I'm stuck, so I thought you guys could help me solve it . I'm trying to make my first game project and basically everything works fine but when I press the start button a prefab window appears and I don't really know why, I'd like to make an introduction scene instead but I cant remove it. Thank you for taking the time to read this, have a good day.

 

no answer ? please if somebody have a clue it'll be nice to share it