Who will prepare FRS (functional requirement documents)? What is the important of FRS?

The Business Analyst will pre pare the FRS.
Based on this we are going to prepare test cases.
It contains
1. Over view of the project
2. Page elements of the Application (Filed Names)
3. Prototype of the of the application
4. Business rules and Error States
5. Data Flow diagrams
6. Use cases contains Actor and Actions and System Responses