What I find shocking or, well, confusing, is the fact that things usually come into existence inside reality. Here we're talking about the coming into existence

What I find shocking or, well, confusing, is the fact that things usually come into existence inside reality. Here we're talking about the coming into existence of something that it's easy to consider (I don't know how correctly) reality itself. How does that come out of nothing? And what even is nothing, outside reality?