How do I generate these kind of summaries in Visual Studio?
///
/// Returns a number
///
///
Like George says, /// on the line just above will autogenerate it.
Beyond the boilerplate comment template it gives you, I'd recommend taking a look at the other tags you may use: http://msdn.microsoft.com/en-us/library/5ast78ax.aspx
This may be used in combination with other tools such as Sandcastle to automatically build CHM guides, etc.