The feature is named XML Documentation Comments and is documented here. It appears to have been modelled closely on the equivalent .net feature so you should be right at home with it.
The documentation contains this example:
/// <summary> Removes the specified item from the collection
/// </summary>
/// <param name="Item">The item to remove
/// </param>
/// <param name="Collection">The group containing the item
/// </param>
/// <remarks>
/// If parameter "Item" is null, an exception is raised.
/// <see cref="EArgumentNilException"/>
/// </remarks>
/// <returns>True if the specified item is successfully removed;
/// otherwise False is returned.
/// </returns>
function RemoveItem(Item: Pointer; Collection: Pointer): Boolean;
begin
// Non-XML DOC comment
// ...
end;
which results in this help insight hint:
And there are various other ways to process and consume the documentation.