Enchantment

Armour Enchantments

The Protection enchantment is effective against all types of damage, but the specific enchantments are stronger: if you’re fighting Skeletons, Projectile Protection IV will be better than Protection IV.

Protection

Makes your armour more protective. Max level IV.

Fire Protection

Reduces damage from fire; reduces the length of time you stay on fire. Max level IV.

Blast Protection

Reduces the effects of explosions. Max level IV.

Projectile Protection

Reduces damage from arrows and fireballs. Max level IV.

Helmet Enchantments

Aqua Affinity

Allows you to break blocks more quickly when underwater (works better when standing on the bottom than when swimming).

Respiration

Increases the length of time you can stay underwater before drowning. Max level III.

Chestpiece Enchantments

Thorns

A chance of damaging your enemies when they attack you. Max level III. The level affects the chance of doing damage, not how much damage.

Boot Enchantments

Feather Falling

This enchantment reduces the damage you take when you fall. Max level III.

Depth Strider

Reduces the amount that water slows down your movements by 1/3 per level. With Level II you can swim in water as fast as you cna walk on land.

Sword Enchantments

Sharpness

Increases damage dealt. Max level V.

Smite

Increases damage dealt to “undead” enemies (Zombies, Zombie Pigmen, Skeletons and the Wither).

Bane of Arthropods

Increases damage dealt to spiders and silverfish. Max level V.

Knockback

Increases the distances enemies are knocked back when you hit them. Max level II.

Fire Aspect

Sets the target on fire. Max level II. Use this on your farm animals and they will drop cooked meat! Not so useful in the Nether whaere most of the bad guys are immune to fire.

Looting

Mobs will drop more loot &emdash very useful when killing your farm animals for meat or leather. Max level III.

Bow Enchantments

Power

Increases the damage dealt by your arrows. Max level V.

Punch

Increases the distances enemies are knocked back when you hit them. Max level II.

Flame

Fires flaming arrows, which cause extra damage and can set off TNT. Max level II.

Infinity

Firing your bow doesn’t use up arrows. You still need to carry at least one arrow with you, though.

Tool Enchantments

Efficiency

Increases the speed of mining, digging or chopping. Max level V. An Efficiency V shovel shifts sand and gravel so fast you won’t believe it, and mining obsidian becomes almost bearable with an Efficiency V pickaxe.

Silk Touch

Certain blocks that normally turn into something else when mined can be collected with a Silk Touch tool. For example, grass would normally be turned into dirt, but you can use a silk touch tool to collect grass blocks (great if you want to grow a lawn underground or in the Nether).
Other blocks that can be collected with Silk Touch include Glass blocks and Panes, Ice, Mycelium, huge mushroom blocks and all kinds of ore.

Fortune

Increases the drop rate of items from blocks. Max Level III.
This enchantment lets you get more items from blocks that turn into items when mined, such as diamonds, emeralds, coal, redstone, lapis lazuli, glowstone, melons and flint. A Fortune III shovel turns all of the gravel you dig into flint.

Unbreaking

Increases the durability of your enchanted item, making it last much longer. Max level III.

Fishing Rod Enchantments

Two enchantments are available for fishing rods.

Lure

Decreases the length of time you have to wait for a bite when fishing.

Luck of the Sea

Makes you more likely to cath good stuff and less likely to catch junk.

Source: http://www.minecraft101.net