If you're new to financial ratios, try the online tutorial below from Investopedia. In addition, we have books on the topic ... here's a list in Marqcat, and in the next box, there are links to two online books.
Below are links to some definitions too ...
A full house or a house of cards?
When you need to see how your company compares to other companies in the same industry (peers and competitors), use these sources. Start with RMA e-Statement Studies; it is produced by the Risk Management Association (formerly Robert Morris Associates).
The others are not online! But they're classics, and you'll hear them mentioned regularly. Especially the Leo Troy ...
Thomson One also allows you to calculate industry ratios, but its ratios will based on either GICS or SIC, not on NAICS.