Charms are a type of magic spell concerned with enchanting or conjuring an object.  Charm spells seem to have  inherent powerful positive magic.  A well-chosen Charm is a powerful magical tool against Curses, Jinxes, and Hexes.  The Charms classes at Hogwarts are taught by Professor Filius Flitwick.

Spells that are evil are called Curses.  The Ministry says three curses are"unforgivable," punishable by a life sentence at Azkaban for any wizard who performs them on another human. They are "Crucio," which causes extreme pain (the Latin crucio means to torture or torment); "Imperio," which puts the subject under the wizard's complete control (the Latin impero means to order or command) and "Avada Kedavra," the Killing Curse.  It is the curse that Lord Voldemort used to kill Harry's parents, the one with which he tried to kill Harry, and the one he used to kill Cedric Diggory.  Harry is the only person known to survive it.

As a general rule of magic, successfully performing a spell requires more than just saying a few words. How the spell is spoken-for instance, how confidently-can have great consequence. Casting a spell can require an enormous amount of energy, so a wizard's power is an important factor.

Many charms, spells, and curses are simply Latin words for the desired effect. For instance, "Lumos," the spell that causes a light to appear at the end of a wizard's wand, is a Latin word meaning "light." "Nox," the spell that extinguishes the wand's light, is the Latin word for "darkness."

Latin is used in other places, also. For example, Mad-Eye Moody was once an Auror, a sort of police officer whose job is to bring bad wizards to justice. In Latin, aurora is another word for "light," so Auror is the perfect name for someone who fights darkness. As well, the Hogwarts motto is Latin: Draco dormiens nunquam titillandus ("Never tickle a sleeping dragon").

J. K. Rowling herself has said, "I like to think that the wizards use this dead language as a living language." It makes sense that Latin would be so important. After the Romans conquered Europe (including Britain) about two thousand years ago, Latin became a common language, one that could be used anywhere in the empire. Scholars relied on it to ensure that their work could be shared. It was the also the primary language of Christianity. And for centuries, most books were written in Latin, because every educated person could expected to know it. Many English words estimates vary from 30 to 60 percent-have Latin roots.  Here are a few spells that come from Latin:


Spells Based On Latin

Summoning charm
From the accio, to call or summon.
Makes invisible ink appear
appareo, to become visible or appear
Conjunctivitus Curse
Impairs eyesight
coniugo, to bind together. Eyes have connective tissue called the conjunctiva. When this gets infected, a person gets conjunctivitis, commonly called "pink eye."
Makes things disappear
From deleo, to erase or destroy
Makes teeth grow uncontrollably
From dens, meaning teeth, and augeo, to grow
Splits things
From diffindo, to split or break apart
Opens things
such as the statue of the witch that guards the secret passage from Hogwarts   to   Honeydukes.  From dissiedo, to be separated.
 Invigorates things
 (Oddly, this spell has an effect that is exactly the opposite of its meaning in both Latin and English. In English, "enervate" means to weaken; and its Latin root, enervo, means the same. Neither means energize.)
Expecto Patronum
 Produces a patronus (a guardian)
 From expecto, to throw out; and patronus, guardian.
 Disarms an opponent
 From the Latin expello, to drive out or expel; and arma, weapon
Fidelius Charm
 Places a secret in another trusted person
 From fidelus, faithful, trusted, trustworthy.
Finite Incantatem
 Ends other sprlls
 From finite, end; and incantantem, incantation or spell
 Stops a person or thing
From impedimentum, impediment, hindrance
 Used to travel by Floo from fireplace to fireplace
 From incendia, fire
 Makes a person forget
 From oblivio, oblivion, forgetfulness
Petrificus Totalus
 Immobilizes a person
 From petra, rock
Prior Incantatem
 Reveals the previous spell cast by a wand
 From prior, prior or previous; and incantatem, incantation or spell
 From rictus, a laughing smile
 Makes something seem funny
 Used to dispel a boggart. From ridiculus, laughable
 Repairs things
 From reparare, repair
 Wingardium Leviosa
 Can make something fly
 From levis: light (which gives English word "levitate")

The textbook for this class is The Standard Book Of spells and can be purchased at Flourish and Blotts in Diagon Alley.  Other charm books available there are Anthology of Eighteenth Century Charms and  An
Olde and Forgotten Bewitchments and Charmes. 
Classwork involves  practicing various charms.