The magic of spells work through suggestion. The spells, through images and symbols, feed their associated ideas to the subconscious as a magic effect if we could call it as so.
The magic of spells work through the principle that all ideas tend to materialize, meaning the pass from their existence within the mind to reality, so we are then influenced to carry those ideas to practice. This magic, also, because of the reciprocal influence between spirit and matter, under some conditions, would allow to magically influence what is outside the mind, and we are talking here of effects over matter of magic
One explanation for the magic of influencing the world outside of our minds is based on the theory that objects are not fixed as we perceive them, that are energy that moves spinning around an axis, thus forming vortexes of energy. And under some conditions, the mind would have the magical power to alter the energy patterns of objects, thus changing the objects. This imply the capacity of the mind to focus and channel its energy so it can interact with other forms of energy, thus changing the way the vortex of energy of the object moves, thus changing the object. The images and objects used become the energy channels for that magic interaction to occur.
I have yet to see the above magic to occur with material objects, but yes, I have seen this magic to happen with other people minds, and such is the case for the magic of telepathy.
One word of caution: no magic spell will work unless channels are opened into the external world. By example, doing a job spell will not work unless at least you or someone else let potential employers know that you are looking for one. For healing spells, those will not substitute medical care. And so on for any other one.
Spells usually work in very unexpected ways leading to the results we want. That's why the visualization applied should focus on the desired result, and not in each step thought to bring the desired results of them.
Finally, in this overview about casting them we refer to their use for psychic attacks. These attacks very rarely happen to work despite the repeated attempts of some people to inflict damage to others through them. The negative energy of hate works rapidly against the attacker, also the mechanisms of guilt within the attacker's mind weaken enough the energy that is intended to project.
If you feel the effects of one of those attacks, you had better think that a part of your mind is creating those effects, not someone else. Even if it indeed were so, the only way the sender can influence you is through the same part of your mind that induce the sensing of the psychic attack. This means that healing what causes that sensing within your mind will take care of both possibilities freeing you from an imagined or real psychic attack.
I can help you with individually focused guidelines for casting so you can do them at home.