XML Serialization issues

Been trying to save some item data for an RPG to an XML document, and no matter how I try to implement this it simply just wont work the way I want it to. (Or work at all for that matter)

I want to use the [XmlAttribute()], [XmlElement()], and [XmlRoot()] tag things, but I cant find any good information on HOW to do this. The only "tutorials" I've been able to find are either "Hello World" tier in their simplicity or they're just code without any explanation.

I want to be able to modify the file after build time, and I want to be able to store child classes of the main serialized class in the same file.