This is how we do dcoumentation. Obviously this is in a company context, so I hope it has some relevance.
1. Feasibility study (don't know much about this - never done one). some thing along the lines of Is this humanly possible? Can our computers do it?
2. The next documentation in a project is the Project Definition. This is supplied as the reason for the software (i.e. your teacher has asked you to do a particluar project - this is the project definition)
3. Write a user requirement document.
The purpose of this document is to:
a. Clearly identify all the requirements that must be satisfied by this project.
b. Provide Systems Developers with sufficient detail of the Users requirements to enable them to produce a Software Design Description.
4. Software Design Description. The purpose of this document is to provide:
a. Sufficient detail of the proposed solution to advise Programmers.
b. An estimate of the development time.
c. The basis for acceptance testing.
5. Write a User guide explaining in concise clear non technical language what the software was designed to do and who should use it. Then explain the full functionality of the software.
Documentation seen by many as a chore, is a good habit to pick up if your are considering programming for a job. I hope this may have given you some ideas.