How do i import an entire program into a new screen in another program?

I have developed several levels of a game separately and now I want to stitch them together so that when you get a certain number of points you advance to the next level. I think you set up a new screen for each level but how do you import an entire program to the appropriate level?

Generally it's not a good idea to have a separate screen per level. Instead, store information about the available levels in files and use that information to reconfigure the elements on the screen to conform with the level definition. This allows you to create nearly infinite number of levels.

Thanks - can you elaborate? Why is it not good to use separate screens? I only have 4 levels but I have to get this done by tomorrow, so I need something I can do quickly. Is there a way that will work for 4 levels using screens? That seems like it should be simple.

What kind of files would be used for multiple levels? Unfortunately I have had to pick up everything by doing; I have not had any classes on app inventor.

The general recommended upper limit on number of screens is 10 per app, but different screens are more useful when you have different types/layout of content. Each screen has overhead in App Inventor and so reusing screens for similar content (e.g., game levels) is better than creating a new screen for each variant. For example, you'll have to duplicate your game logic on each screen when you could reuse code if everything were on the same screen. For 4 levels and given the time crunch it's probably fine.

Thanks - so back to my original - how do I load an entire program, sprites, buttons, sounds etc as well as code blocks into each level?

You're trying to do it backwards.
Here is the proper approach ...