Two document templates have been provided.
The first is a Business Requirements Document Template (BRD), which can be used to document business processes and business requirements:
Business Requirements Document Template
The second is a Software Requirements Specification document (SRS), which can be used to document system features, system processes and user interfaces:
Software Requirements Document Template
Your company may already have templates that you can use.
However, if you don't have a template to work with, the above templates are an excellent place to start.
Here is the BRD and SRS in PDF format:
BRD (PDF format)
SRS (PDF format)