If you want to parse your section use:
var config = (SampleConfigurationSection)ConfigurationManager.GetSection("sampleConfiguration");
config.YourCustomProperty = "Hello World";
If you want to iterate through the XML elements manually (which would be a really strange requirement), you could use LINQ to XML
using System.Xml.Linq;
....
var xml = XDocument.Load("path to your config file");
var section = from e in xml.Root.Elements("your section name").Elements()
select e;
If you need dynamic items, then perhaps you could use the ConfigurationElementCollection and then parse your section and work with your collection objects instead of working with the XML directly