Thank-you for your replies, they are appreciated. 
Hmm. 
When I started using Kodular a few months ago, I was using the first blocks in the following image to change screens:
But I had problems switching between screens, so Boban suggested using the third set of blocks in the image. Open Another Screen block Not working - #11 by TwoCanes_LLC
But what works for me now is to pretty much go back to the original method surrounded by a procedure, ie, the middle blocks in the image. 
So my question is when would I ever use the third set of blocks? Why would I close the first screen when opening a second screen if it doesn’t really close until you go back to the first screen? Sorry to be so obtuse, but it’d be nice to understand this issue. 