How do wands and spells work?

[Richard]

Does your victim need to hear you say the spell? Suppose you point your wand a foot over your victim's head, what then? Can you just think your spell without a sound or a wand? Can you victimize your victim if you're way up in the air and the victim is miles away? And how fast does a spell travel? Can people just duck out of the way? Do spells ricochet? Will a trash can lid serve as a defense against a spell? What if you climb into a suit of armor? Would wearing ear muffs protect against hearing a spell? Can a person say "protege aeternum" and have an eternal protection against harm?

[Shobhit]

This is all fictional and depends on the author that how he/she wants it to work

[Richard]

Well, yes and that's just the problem. After some point in the series, I thought to myself "Whatever you say, J.K. Whatever you say." I skimmed over passages dealing with the magic of house-elves and the allegiance of wands. Those talking portraits, I didn't care how they were made or why. It's like listening to Ensign Wesley Crusher explain tachyon beams. It's the magic equivalent of techno-babble.

[Ruby]

I've read the series several times, and there appears to be two types of spells:
1. The kind that takes a material form- jets of light shooting out of the wand. Attack spells like Expelliarmus.
2. The kind shown in the movies- things just happen without the jets of light. Windgardium Leviosa, I'm thinking.

What happens is that a wizard has magical power, and the want is the instrument that helps channel that specific wizard's power into a spell. It doesn't depend on the words being said- or else nonverbal spells would be impossible (and they're in the sixth one). It depends on concentration (thinking the words) and the correct wand movement.
I believe that with the jets-of-light spells, your aim matters more. Take Avade Kedavra- the killing curse is a jet of green light, and we've seen in the books how it 'hits' people's bodies, throwing them in the air. Also the torture spell, crucio- in one scene in the sixth one, this spell misses its target and hits a wall. Spells ricochet, but depending on the spell, what you're using as a shield could be hit by the spell and change. Like if someone is trying to transfigure you into a ferret, and you push a trash can in the way, the trash can would probably be ferret-ized instead.
If you don't do a non-jet spell correctly, it just doesn't work. Take silencio, the silencing charm. When Ron does it incorrectly, the bird just shrieks.

My guess is that for the jet spells, they can go farther because it's like shooting an arrow. With the ones that don't have jets, you probably have to be able to see what you're doing, or else you can't concentrate. And hearing a spell has nothing to do with whether it works on you.
And spells aren't made up. They have specific roots and things. So even if something sounds like a spell and you concentrate, it may not work. So that protego thing would be like yelling, "hocus pocus!"