User story advice

As part of a project I’ve been asked to write a detailed functional specification for a particular component of a website. 

Highly detailed functional specifications are very typical of a waterfall way of documentation. Is this an Agile project you are working on? 

Since your question is on a user story and it appears what you are trying to document is pretty extensive, you may have to decompose the work into multiple stories. These could be coherent stories that align to a specific functionality and could be grouped as a feature.

The typical user story format is "As a < type of user >, I want < some goal > so that < some reason >."

So for example, you could write something like "As a visitor to the website, I want to view the different products by price range, so that I can choose the item relevant to my budget".

Now, you're acceptance criteria should be everything that would make sure the above functionality works and it should be testable (ideally speaking).

As a guideline (strictly a guideline only), you'd want to write a story such that it fits onto an index card (3 by 5 inches). The front of the card should accomodate the description and the back should be used to fit the Acceptance Criteria.

Hope this helps.

So I’ve been given the user story and a screen shot of the component of the website. 

It’s the documenting of the functional specification of the screenshot which I’m unsure about how to approach. 

As part of a project I’ve been asked to write a detailed functional specification for a particular component of a website. 

What are the expectations regarding how this detail will be validated?

Don't forget a user story is basically just a reminder for a conversation to have among the people interested in user's needs.

=> rules of the 3 C's : Card / Conversation / Confirmation

In addition to Ian's question, I would also suggest focusing on the "what" (the requirements) and not the "how" (what I think a functional spec is).

So ask yourself/the PO/stakeholders what the component is meant to achieve.

What is the level of detail you're asked to describe? Is there any flexibility to experiment or to add to the empirical process Scrum embodies?

As part of a project I’ve been asked to write a detailed functional specification for a particular component of a website. 

A bunch of questions:

• Who is requesting this information?   
• Do you know the reasons why they are requesting it?
• What is your role in this "project"? 
• Is Scrum being followed in your organization?
• Is the Development Team better positioned to provide such solution-based content?