I know that most of you have already learned how to cast spells, but in case you are having trouble, Ill try to explain best I can on how to cast a spell or charm.
Note that some spells/charms need certain items to be cast.
Step 1 ) Say your spell/charm's incantation
The Incantation is the spell/charm's name.
Step 2 ) Begin casting your spell by left clicking anywhere on your screen
I would recommend straight forward since you still have to do your spell/charm's movements..
Step 3 ) Complete all of your spell/charm's movements
Some of these spell movements may include:
-Swish Up ( Look up and right click )
-Swish Down ( Look down and right click )
-Swish Up Right ( Look up and then a bit to the right, right click )
-Swish Up Left ( Look up and a bit to the left, right click )
-Swish Down Right ( Look down and then a bit to the right, right click )
-Swish Down Left ( Look down and then a bit to the left, right click )
-Swish Left ( Look left and right click )
-Swish Right ( Look right and right click )
-Jab ( Right click )
Step 4 ) Finish by left clicking once again
If once you have finished it says "Spell Unsuccessful" then that means you are casting the spell/charm right, you just need to practice that spell/charm more.
Something else that may pop up is "Spell cancelled due to whooshing instead of swishing". This does mean that you are doing something wrong, but it could be simply that you left clicked twice and didn't realize it, or did the spell/charm to fast.
Remember, all spells/charms need to be practiced no matter what the difficulty. It takes time and patience so don't worry if you haven't mastered the spell within ten minutes of casting.
Another thing to remember is that no matter what spell/charm you're doing, you always have to left click when beginning and finishing your spell/charm.
I hope this helped.. and if I got something wrong then feel free to correct me.