The "how" of magic is a very difficult question to answer. Really, you'll get vague and very differing answers from people.
There's a quote out there somewhere about synchronicities which I think rings true for much of external change in compliance with will. I do not remember the exact wording or who said it, but it is along these lines:
Synchronous events (meaningful coincidences; things which seem to be connected to a particular working, or even signs from the supposed supernatural) are things which we decide after the fact are synchronicities, unless we decide they are just coincidence.
So let's say you do some work to attract money. In the next few days you find $20 on the sidewalk. You have a choice to believe, afterwards, that it was in response to your work. Or you can tell yourself that you found it because people drop money all the time.
I believe internal magic is different, in a way. Magic, being change in accordance with will, is something which can be employed to develop as a person. But it can take whatever name you give it. Every time you enforce a behavior, you create or strenghthen neural connections related to that behavior.
So let's say someone wants to tame their temper. They begin to meditatie, which has proven benefits. They also start playing scenarios in their mind, as vividly as they can create, even reliving moments in their past. In these scenarios, they recall things which pushed them to anger. In stead, they in their visualization keep calm and respond rationally or even keep silent. They begin to analyze their own behavior, and recognizing their physical responses of the subconscious anger rising to the top, before they get angry. They learn to redirect their emotions at that point.
They study mindfulness, of observing thoughts and emotions but not getting involved, experiencing only those things which thwy choose to, while acknowledging the others but letting them pass.
Eventually the person starts seeing they remain calm when they used to go off. Thwy have affected a change in compliance with their will. There's not much more magical than that.
If a person believes it is in part due to spirits, gods, or quantum entanglement, or that the (nebulously defined in terms of sublety) energy they exerted caused a result, does it really matter?