Now I want to import a math module so that I can use some of its functions while reading data from a XML file.
That sounds reasonable. So your first task will be to find an implementation of the math module for namespace http://www.w3.org/2005/xpath-functions/math that XQiB / MXQuery can process, install it on your server, and point to it from the module import statement, as shown in the module import example on the XQiB web site.
Or alternatively, you may decide that you can work with the math functions in http://www.zorba-xquery.com/zorba/math-functions, which MXQuery (and thus XQiB) appear to support natively. (I see this in the MXQuery documentation but not in the XQiB documentation, so I guess there is the theoretical possibility that XQiB is using an older version of MXQuery -- but it's more likely that the development team just has better things to do with their time than document modules already documented elsewhere.)