A traditional requirements process includes identifying, assessing, documenting, and validating the requirements. If validation fails, the processes repeat until enough clarification is obtained.
Requirements identification determines what the site should do, what tasks it should support, the types of information it should contain, and the types of interactions it should allow, to name a few. During assessment, you evaluate the requirements collected to ensure they are a clear, complete, and unambiguous description of what you need. Documentation can take many forms.
Depending on how you collected the requirements for your site, documentation can be well on it way. Documentation can be in the form narratives, use cases, diagrams, models, and even site mockups (prototypes). Once the requirements are documented, they should be reviewed to ensure that statements and requests were not misinterpreted. The more descriptive the documents, the better chance you have in validating that you have the solution desired.