whether you are a beginner that is totally NEW to a sewing machine or the classic OLD hand...you can always learn more when it comes to sewing machine needles and their proper uses.
Here are two sites that I use as resources.
http://sewing.about.com/od/sewingmac...Sizes.--94.htm
http://www.schmetzneedles.com/Schmetz_Sales_Guide.pdf
I keep this chart on hand to give to people who want a reference guide. I also have the Schmetz pocket guide book.