the great knowledge of /prog/ i besiege thy

Oh great base of the programing knowledge of the internet know as /prog/ i come here as a final source for my question...
im a noob programer... and as such im unable to do many things... ive need to open an xml file and append a node to it but using xmltextwriter in c#... this is probably easy for you all and i would normally never post here but i havent gotten any other usefull answers anywhere else...

amm entripse can suck nuts... this is for school and i dont need no enterprise shit to fix it....