XML is an information format. It is up to the website or database owner to develop a way to use the data defined in the XML file and to decide how they will store the information in their own database or on their system. Often shopping cart systems or web portal systems will have a module which will allow the use of xml imports. Sometimes a shopping cart system will need to develop a script or program in the programming language of their choice which will read the xml file, parse it (match the info to their own needs) and then insert the data into their own database.
If your shopping cart system does not have a way to import xml, you may need a programmer to build a program for you to import the data. There is third party software which will allow you to change the format of the xml file. Perhaps one of these will transform the xml file into another format which you can import.