Spells are used in dueling and fighting. Some of these include Stupefy, Impedimenta, Flipendo and Expelliarmus. In the battle of the Department of Mysteries Harry and his friends Hermione, Ron, Ginny, Neville and Luna fight the Death Eaters using spells like these that they learnt in the D.A, otherwise known as Dumbledore's Army. Harry also uses the spell 'Expelliarmus' when he creates the Priori Incantatem with Lord Voldemort in third task of the Triwizard Tournament, in Harry Potter and the Goblet of Fire. Harry also discovers new spells such as Sectumsempra and Levicorpus, which were invented by the Half-Blood Prince, also known as Severus Snape, undercover teacher at Hogwarts School of Witchcraft and Wizardry until Harry Potter's sixth year and one of Lord Voldemort's most loyal servants. Most of this kind of magic can be learnt at Hogwarts and is taught in the Defence against the Dark Arts classes from years one to seven.
Curses are used in dueling, and are usually for badly hurting the opponent or even killing them. Probably the three most famous curses are the Unforgivables. These are: Avada Kedavra, the killing curse, The Imperius Curse, which is used for controlling, and The Cruciatus Curse, which tortures your opponent. All three of these Unforgivable Curses are illegal and you are sentenced to life in the Azkaban prison if you are caught using them on any wizard or muggle. Some other curses include Locomotor Mortis, which locks legs together, Furnunculus, which produces boils on your opponent, and Cunjuctivitis, which is used for damaging eyesight. These three curses, just like the Unforgivables and any other curse are very dangerous and can cause serious damage to your opponent or any other innocent bystanders such as other wizards or even muggles.