My question has two parts, and it has to deal with drawing data flow diagrams and models.

My question has two parts, and it has to deal with drawing data flow diagrams and models. 

Part 1

I need help and a demonstration with modeling a relationship between employees and managers in a company. This relationship can be demonstrated in a unary or recursive relationship on the employee entity. 

Something else I don't understand is how I would go about modeling the cardinality of the unary relationship to indicate that an employee has one manager and a manager may have many employees. The model demonstrated must show that an employee must have a manager and the manager must have at least one employee. Further, and something I am getting stuck on is, if my manager has only one employee assigned, and then that employee is reassigned, what happens? The relationship drawn needs to be done so with cardinalities to indicate that a manager may have no employee. 

The second part of what I need help with is as follows:

Part 2:

Assume I have an organization and my boss asks me to create a data model for employees participating in various projects. It is possible that one employee can participate in many projects, and one project can have many employees assigned to it. My stakeholders want to know the role of each employee on a project. 

Furthermore; I need help with an explanation of which type of entity will help me model this many-to-many relationship.

And is it possible for a project to have no employees assigned, and if so, what is the most effect way on how to model that possibility?

And is it possible for an employee to be unassigned to any project, and what is the most  effective way to model this possibility?