Creating help documentation for my asp.net application

I have developed a web application in asp.net and for that I need to create help file. I want give a detail help for the user for each page with explaining the fields and buttons in that page. Also need to show the entire documents as help files as chm file when we press F1 or click the Help menu in the application. I have not done this before so I do not have any idea on this. I browsed this here and some suggested using sandcastle and other documentation tools. I wanted to know whether I need to create a project for help in my current application and store the help content in the database?