If you mean by "magic words"
, barbarous names or whatever you call it, magicians probably won't understand them themselves.
The Greek Magical Papryri are thick with them; there are basically three schools of thought:
1. These barbarous names
do have meaning, they are corrupted words and phrases from dead or obscure languaged, similar to "hocus-pocus" which is a garbled version of the Latin transsubstantion prayer used in Catholic mass ("Hoc est enim corpus meum").
2. They don't have meaning (
see discussion here) but purely performative value, geared towards putting the magician (and also his audience, for example during a healing) in a special frame of mind.
3. They have hidden meaning that can be decoded by numerology or attributing planets, signs of the zodiac, etc. to the consonants and vowels, a view that is e.g. espoused by Michael Kelly in his
"Words of Power".
Depending on the context, words you don't understand may arouse different feelings, ranging from awe (because they sound impressive) to open hostility ("Somebody's gabbing at me in a foreign lingo!"). Against a suitably ritualistic backdrop, these words may in fact have power over the audience but they might also sound silly if you're unable to convey a certain sense of solemnity; it's also the performance of the ritual that counts. First of all you need to convince yourself that you're doing something meaningful and spectacular; impressing others will not depend on the words alone but also on gestures, charisma, props, etc. On the other hand, knowing the meaning of a word that others don't automatically gives you an edge, knowledge being power and so on.