There are two ways to functional requirements:
Basic implementation
As the name says, basic implementation is discussed, for example: what would be done and how it would be done.
Enhanced implementation
This approach can be used when working with the enhancement of the system. The purpose of the implementation is to enhance the existing features, create new features or bug fixing.
Both approaches can be implemented in one phase or multiple based on the requirements. It is also essential to keep the stakeholders on track and involve them during the development of business objectives. It is possible to use templates provided by Microsoft to document the requirements and follow-ups.