When you are ready for your game to progress to a new chapter, you can use the *finish command. This can go inside an #option like the *goto command, or anywhere else. Make sure that your scene list (in startup.txt) has the chapter name (the name of the .txt file) that comes next
Your other option is to use *goto_scene. To use this one, format it like: *goto_scene text_file_name.txt. You can put this command under your #option or anywhere else
I want to give you a few resources that will help you learn how to use choicescript.
When you need help, try using the search feature to find threads that might help you. If you search for the error message you are receiving, like “It is illegal to fall out of a *choice statement, you must *goto or *finish before the end of the indented block” that you mentioned above, you will probably find threads about that issue, many of which will have solutions that hopefully help you