I've never had one personally, only worked with children that had them. So if you have any questions that don't require a personal perspective, let me know and I'll try to answer them for you.
Here are some links to more information:
http://www.medhelp.org/medical-information/show/2716/Feeding-tube-insertion---gastrostomy
http://video.google.com/videosearch?hl=en&client=firefox-a&rls=org.mozilla:en-US:official&hs=Spp&q=g+tube+feeding&um=1&ie=UTF-8&ei=iyVvSp3xF4PYsgPOs-HwAg&sa=X&oi=video_result_group&ct=title&resnum=10#
http://www.upmc.com/HealthAtoZ/patienteducation/Documents/GastroTubeFeed.pdf
I too have no personal experience with this, but I would imagine that a g-tube would be a good option for a patient with little ability to obtain adequate nutrition on their own. I'm sorry not to have any further information to offer, but perhaps another member of our community will be able to jump in with a personal experience of their own.
I have had experiences with feeding tubes they sound all great and everything butreality hitswhen you actually have it in there, at frst I had an ng tube, but I couldn't get over the gagging response from having it in, they pulled it (that's no fun either)then they put in a J-tube, so it going through jejunum,etc but (for me) I can't stand foreign things outside my body, I was going crazy with it, I told them to pull t out or I would. It was painful to have something pulling on you everytime you moved, walked or even shifted in bed, it's a never again for me! But maybe someone else will have a different experience than I did, if I could have stood it longer it does actually get some nutrition in me. I am so sorry you seem too young for all these problems aren't we all, bless you heart good luck.
Suzanne