For detailed info on modules, look at the
wiki page.You can see the shield strengths and other info also at the outfitter websites:
http://www.edshipyard.com/
http://coriolis.io/
General rules:
internal modules
1. E is always the worst and A is always the best at what the module does. E.g. in case of shields the E rated is the weakest, D is stronger than E, C is stronger than D, and so on.
But this is valid only if you compare ratings within the same class (size)! A bigger class shield will be usually stronger than a smaller class one, even if the bigger class is lower rated. E.g. on a Cobra, a 4D shield is stronger than an 3A.
2. Power consumption always goes up from E to A
3. The weight of modules: E, C, A have the same weight. D is lightweight modules (40% weight). B is hardened modules (160% weight), they supposedly can take more punishment before failing.
4. Power plants have an efficiency attribute. This shows how hot your ship will run. E power plants run hottest, A are the coolest. This matters a lot when you are fuel scooping or shooting beam lasers for a long time.
weapons
There are many quality ratings but they don't matter in fact. There is only one quality rating for each size and type of weapon. E.g. only one kind of class 2 gimballed pulse laser exists (2F). Only look at the size and weapon type, you can ignore the letters.