Marlins,
There is a sample that does what you are asking at this discussion:
https://community.articulate.com/discussions/articulate-storyline/free-sample-restricted-and-free-random-navigation-using-variables-and-triggers
The Restricted version won’t allow the learner to advance until all layers (actually the sample uses different slides, but the principles are the same) have been visited in order. The free navigation allows the learner to visit the layers in any order, and advance at any time. The mixed version allows viewing the content in any order, but requires it all be visited before advancing.