Protection will stack on different armor pieces, and provides comprehensive protection against all forms of damage except The Void and server kill commands. It is true that falling, fire, lava, poison, and even mob damage will be reduced, but false that the armor durability will always reduce more than normal. When falling off a building with Protection IV boots, the boots will not suffer any damage, producing the same results as feather falling III boots. The Armor will take more damage from Mobs and Players however.
It is possible to get feather falling IV AND protection IV boots, reducing fall damage immensely. All other pieces of armor with protection will add additional damage reduction in the same way the boots would. Protection appears to be one step down from specific defenses (ex: Protection III = Feather Falling II when taking fall damage, or Protection III = Fire Protection II when in lava).
TL;DR- Protection enchantments are slightly less effective than specific ones, but protect against everything at once. The best possible armor would be:
Helmet: Respiration III, Aqua Affinity I, Protection IV, Thorns III
Chest and legs: Protection IV, Thorns III
Boots: Protection IV, Feather Falling IV, Thorns III
Note that Only highest Level of Thorns take effect if present on multiple peices of armor. Source
The symbols in the enchanting table have no relation to the actual enchant it yields; they are randomized.
You can translate them, however. The symbols are from Commander Keen's Standard Galactic Alphabet:
Again, though, the sentences and phrases are meaningless. Your enchants are random (well, sort of, as of Minecraft 1.8). Good luck.
Best Answer
Aqua Affinity allows the wearer of the enchanted helm to mine (break blocks) faster while underwater. Normally, being underwater slows down this action considerably. It also works while you're on ladders or otherwise suspended.