Expecto Patronum

Expecto Patronum, probably one of the most famous charms of all time and the most used of them in Harry Potter and the Prisoner of Azkaban is mainly used to fight off dementors, large, strong, cloaked creatures with no face of actual body that were hired by the Ministry of Magic to guard the wizard prison, Azkaban. Although, these creatures also try to suck all of the happy memories from your brain or give the deadly and most harsh death, the dementor's kiss.

Rating
6/8-Expecto Patronum is a very hard charm to conjure, especially at a young age, like Harry Potter.

Appearance
The Expecto Patronum charm at its most powerful is a large blue light coming from your wand in the shape of a massive funnel, or even a wave of light blue magic shooting across the sky clearing away dementors in it's tracks. It may also take the form of an animal, not of your choice, but and animal that will suit you and you Patronus. Harry's Patronus is a stag, representing his father's animagus form, while Hermione's is an otter and Ron's takes the form of a small Jack Russell Terrier.

Learning
Expecto Patronum, the Patronus charm is a very hard spell to learn, especially at a young age. Before you cast the spell, you must think of a happy memory, which fills up your brain, and make sure you are completely focused on that particular memory. Once this memory is in your mind, hold your wand up into the air, and without moving it, point it towards the Dementor and say clearly 'Expecto Patronum!'

Prisoner of Azkaban
In Harry Potter and the Prisoner of Azkaban Harry's Patronus charm is one of the most used spells. Harry casts his first Patronum in Professor Lupin's office one quiet night. At first he fails to fend away the Dementor, and faints, but wakes up to find Professor Lupin waiting for him on the ground. Harry persuades the teacher to allow him to try again, and luckily, Harry succeeds. His Patronus charm fought of the Dementor, but he was told that the real thing is much harder. Later that year, when he meets his godfather, Sirius Black, is the next time when he uses 'Expecto Patronum'. Down by the lake a crowd of nearly one hundred Dementors surround him and his fainted godfather and almost dies until he sees what he thinks is his father over on the other side. The mysterious stag Patronus fights off the Dementors, and it was not until he traveled back in time after the incident that he realized that it was actually him casting the Patronus in the future.

Order of the Phoenix
The next and only other time Harry uses his Patronus charm is in Harry Potter and the order of the Phoenix. Dementors attack in the streets of Little Whinging, Surrey when Harry and his cousin, Dudley Dursley, are running home. Harry is pinned to the wall by one Dementor, while Dudley slips over and is amazed because he thinks Harry is flying;muggles can't see Dementors. Finally, Harry pulls out his wand and pokes the Dementor off him. There is a flash of blue light when Harry uses the Patronus and the Dementor is gone. The charm is shot back at the second Dementor who had recently been taking all of the happy memories from Dudley.