The requirements traceability matrix is an extremely important tool for the project. Requirements define customer expectations and the traceability matrix allows the team to follow each requirement through the Project Mgmt. Life Cycle (PMLC). The team elicits requirements from the customer and then moves the requirement through design, development, testing and implementation. This tool helps the team to audit the project as well during the PMLC, and take a litmus test, Are we delivering what the customer has requested?, thereby avoiding costly rework and unwanted change requests. Additionally, the traceability matrix assists the team in analyzing the impact of changes to requirements during the project.
You want to provide the appropriate level of detail while maintaining a reasonable number of requirements since you will base your planning and scheduling on these requirements.  While there is no minimum or maximum number of requirements, the expectation is that most students will have somewhere between 3-7 high level requirements which will then be used as the basis for the Work Breakdown Structure (WBS). 
At a minimum, you should identify several high level requirements, functions, and features.

Note: This is a online retail grocery web application project. I already did project charter and I will share the document.