In Minecraft, you can enchant a number of things. Among these are: Armor, weapons, and tools. Even other un-enchantable objects can be enchanted with a mod/plugin. Legitly, the highest level enchantment is Level 30. (50 was the highest a few versions ago.) The largest number certain mods can enchant is 127, but with other mods, you can enchant 20,000+. Legit enchantments (Level 30 max.) are displayed in Roman Numerals, a.k.a. I, II, III, IV, and V. (In this order: 1, 2, 3, 4, and 5.) To legitimately enchant an item, you must first have an enchanting table. Enchanting tables require: 4 obsidian, 2 diamonds, and one book.

To get the highest possible enchantment legitimately, you must build a 4x4 box of bookshelves, leaving a 3x3 gap of air within the box. (Floor does not require bookshelves.) break a hole in the middle of the of one side, and place the enchanting table in the middle. Simply right click the enchanting table and place the item in the slot.

Example enchantment.

Glyphs flowing from the bookshelves.
The enchantment table uses different alphabet, nicknamed 'Galactic Alphabet.' Below is the translation for the new alphabet in Minecraft.

Galactic Alphabet Translation. ^^