Here is an example of the working app
Your task is to recreate this using Behavior Driven Development.
This project is likely larger than anything you have tackled thus far. Work slowly and iteratively. Often this means to get a specific feature working in a purely functional way and then refactor to an OO approach. If your group can manage to build out all the functionality without creating instances, more power to you, but it is very likely that at some point you are going to wish you could say list.tasks. This is your world, build a structure that works for you.
(i.e. a list has many tasks, task belongs to a list)