Maximum UV protection would be to paint your sunglasses black so no light of any kind gets through :). I suspect that what they mean is something like “Our sunglasses offer the highest level of UV filtration available today.” I’ll let someone like PapaBear explain the difference between UVA and UVB. As for knowing what kind of protection your shades give, your best bet is if they tell you on the tag. I suppose that you could set up some kind of standardized experiment where you measured how much UV light was filtered out by your sunglasses, but that would be alot of trouble, unless you have a UV source and UV meter conveniently at hand. I don’t know if there’s any kind of consensus as to what level of filtration is necessary, so even if you did this experiment, it might not be very useful.
“I had a feeling that in Hell there would be mushrooms.” -The Secret of Monkey Island