I've built an app to do what you want. It's simple enough. The screen at startup and the blocks are posted below.
But I must admit, I've been using App Inventor for over 12 months and when I started the concepts and terminology were confusing. Can be enjoyable though.
I haven't tested it. There'll probably be a bug or two. Can you make sense of any of it? Does it encourage you to dip into App Inventor?
