There is too many to list, but here is a few:
Alohomora
Incendio
Aguamenti
Expelliarmus
Wingardium Leviosa
Langlock
Muffliato
Episkey
Sectum Sempra
Accio
Expecto Patronum
Lumos
Nox
Levicorpus
Harry and his friends don't use this, but Avada Kadavra
Crucio
Imperius
Impedimenta
Stupefy
Repairo
Hope that's enough for you!
p.s.
don't rely on the spelling; it is likely not correct
Read Harry Potter
To put is simply, they are friends.
Yes, some of them do, including Hedwig.
Lumos Levicorpus Langlock Legilimens Liberacorpus Locomotor
here are some: Stupidfid Exspelleamus Expectopatrollum
Some of them are based on mythology, folklore and Latin but all were invented by J.K. Rowling. They are not real.
Yes, the Harry Potter books. If you want more details about each spell and potions, please note that they are fictitious and won't work as in the books, so you can just as well make up your own spells and potions. In any case, there are references on the Web that collect all the details known from the books. You can find some things in the Wikipedia, or in the Harry Potter Lexicon.
In my cases, you can look for some or teachers magicians and maybe I think watching the all the harry potter movies.
Crucio is the most commonly know painful curse. It inflicts the worst pain amongst it's victim.
Wikipedia has a list of many of the spells; search for "Harry Potter Spells". Several fansites also list the known spells; for example, the Harry Potter Lexicon (hp-lexicon.org). Please note that none of the spells work in real life; they are part of a fantasy story. Also, not all details about each of the spells are known; the sites mentioned, and others, only list details that appear in the books, for example, the exact words to say, if it has been mentioned in the books.
Avada Kedavra, Stupefy, Sectumsempra, Wingardium Leviosa, Aguamenti, Accio, Alohomora, Crucio, Expelliarmus, Expecto Patronum.
Easy, you get some Harry Potter stuff. Read ALL the books in ORDER and go to all your friends and say or yell ( your choice) that your now an OFFICIAL fan!:)