Please refer this article it has nice explanation. it will clear your understandinghttps://www.guru99.com/c-sharp-serialization.html

XML serialization serializes only the public fields and property values of an object into an XML stream. XML serialization does not include type information. For example, if you have a Book object that exists in the Library namespace, there is no guarantee that it is deserialized into an object of the same type.NoteXML serialization does not convert methods, indexers, private fields, or read-only properties (except read-only collections). To serialize all an object's fields and properties, both public and private, use the DataContractSerializer instead of XML serialization.The central class in XML serialization is the XmlSerializer class, and the most important methods in this class are the Serialize and Deserialize methods. The XmlSerializer creates C# files and compiles them into .dll files to perform this serialization. In .NET Framework 2.0, the XML Serializer Generator Tool (Sgen.exe) is designed to generate these serialization assemblies in advance to be deployed with your application and improve startup performance. The XML stream generated by the XmlSerializer is compliant with the World Wide Web Consortium (W3C) XML Schema definition language (XSD) 1.0 recommendation. Furthermore, the data types generated are compliant with the document titled "XML Schema

1). The XmlSerializer constructor generates a pair of classes derived from XmlSerializationReader and XmlSerializationWriter by analysis of the classes using reflection.2). Temporary C# files are created and compiled into a temporary assembly and then loaded into a process.3). The XmlSerializer caches the temporary assemblies on a per-type basis as the code generated like this is expensive. This cached assembly is used after a class is created4). Therefore the XmlSerialize requires full permissions on the temporary directory which is a user profile temp directory for windows applications.

It get the properties from an object and transform it in XML. But the object must be declared as [Serializable] on class definition. If you don't want a certain property to be serialized you must put up in his declare [XmlIgnore].

The XmlSerializer constructor generates a pair of classes derived from XmlSerializationReader and XmlSerializationWriter by analysis of the classes using reflection.