If you have no idea about anything about it, I suggest you first start to learn about xml and xsd, it will help a lot to communicate with others about the subject. There are some good tutorials
here[
^]: you have to look in the XML section, there is an entry about xml and an entry about schema (xsd).
Once you understood a bit more the subject, tell us what you need to do precisely. If you only need an XML parser, there are some lightweight libraries that do that. But I guess you also have to validate using the xsd ? Do you need to do generate C++ classes from your xsd file ?
The link you got from the previous poster is good, but this is a commercial product, I don't know if this is acceptable in your case ?