Please tell us how you created the nav bar. Menu? Buttons? Graphics?How do you know they have finished a chapter?Generally, you just cover the parts you don't want them to access with a transparent shape and then hide once they have visited the chapter. You will probably need to set a variable. Add "a" to a variable for the first chapter, b for the second, etc. Hide first one if variable contains a, hide second if variable contains b, ...
