The Marvel Cinematic Universe is full of miraculous feats. Technological advances the likes of which we could only dream of have made heroes and villains out of men and women, but technology isn't the only tool for creating Earth's mightiest heroes. Magic has also created legendary figures such as Thor, Doctor Strange, and Scarlet Witch, as well as other big names in the MCU. Unlike technology, however, magic is something that is only shaped as an idea in our minds. While we might not have any trouble believing a real-life Iron Man suit could be made given enough time and money, very few people would go on record to say it's possible to develop supernatural powers. Can such an abstract concept truly be explained, and how does the MCU attempt to handle such explanations?
The most important takeaway from the MCU and its explanation of magic is that it varies. No one method is concrete, and it seems that multiple explanations for magic can be simultaneously correct. For example, Black Panther makes use of the Astral Plane, something that is inherently magical but not entirely explained. Despite the lack of an explanation, it canonically exists, and its existence is not impeded by explanations of magic in other films, nor do those explanations necessarily clarify how the Astral Plane exists. A similar plane of existence is seen within the ending of Avengers: Infinity War when Thanos (Josh Brolin) finds himself in an ethereal realm with a young Gamora (Ariana Greenblatt), but it is not explained whether these two realms have any connection, and Thanos is seen right after being exactly where he was on Earth. So, while they are both canon and act similarly as one another, these two magical planes of existence are likely completely separate. To put it simply: magic is not tied to one form of existence. It can be manifested in various ways, and those ways can coexist without being reliant on one another.
The first time the Marvel Cinematic Universe introduced magic into its canon was 2011's Thor. The film centers around the godly being Thor (Chris Hemsworth) and his time on Earth after being cast out by his father Odin (Anthony Hopkins). While the movie itself does not explain much about how Thor's powers work, he notes at one point that what we on Earth call magic and science are the same thing where he is from. To him, there isn't really a difference between the two. This helps us to understand how magic is perceived by those who use it all the time, and it is important when trying to understand just what magic is. So for Thor, understanding how his brother can manifest himself into different forms is just like how we would understand a scientist's ability to make two liquids spontaneously explode on contact with one another.
Another important time that the MCU introduces us to magical beings is Avengers: Age of Ultron with the presentation of Wanda and Pietro Maximoff (Elizabeth Olsen and Aaron Taylor-Johnson, respectively). These two develop supernatural abilities after being exposed to the Mind Stone in experiments performed by HYDRA. Their abilities are tied to an item of mystical power, and thus it is the Mind Stone itself that is the source of magical energy. While they do not need to use the Mind Stone as a source of energy to utilize their powers, it is still proof that magical abilities can be granted to those who were otherwise powerless before. Canonically, in the MCU, magic is both something that can be granted upon users and something that can be harnessed by those with innate magical properties such as Thor. While it is true that Thor had to learn and comprehend how magic is utilized, it is also true that he was born with magic within himself, just as we can understand science but are still born with the innate presence of science within us through cells and chemical reactions and the sorts.
Without a doubt, the most in-depth explanation for the presence of magic within the MCU has to come from the film Doctor Strange. In one scene of the film, the Ancient One (Tilda Swinton) explains to Dr. Stephen Strange (Benedict Cumberbatch) how they harness and use magic. For them, spells are created as follows: "We harness energy drawn from other dimensions of the multiverse to cast spells, to conjure shields and weapons...to make magic." The Ancient One describes spells as being synonymous with programs, "...the source code that shapes reality."
In this way, it is elaborated that spells are not necessarily usable only by those gifted with innate magical properties, but by anyone given enough time and practice with the arts. This lines up similarly with the concept provided for Wanda's ability to use magic, though in her scenario the magic was not learned but rather granted through experimentation. For Stephen Strange to become as powerful with magic as he is depicted in later films, he had to study and practice a multitude of spells and rituals. It is the same concept as someone going to college for something like Biology. The more one learns of a subject, the more their ability to implement and utilize that subject grows. Where the similarity stops perhaps is when Doctor Strange makes use of the Time Stone. This connection between the ability to study magic and the innate magical properties of an Infinity Stone shows that the combining of two different properties is possible to enhance magical abilities.
Things get more complex once you start factoring in things like Star Lord's celestial being of a father Ego or the existence of the Infinity Stones in the first place (their existence is more or less explained in Avengers: Infinity War as being crafted from the Big Bang) or even the entire concept of the Multiverse as seen in recent MCU pieces of media such as Loki and Spider-Man: No Way Home. No matter what the origin, the overall takeaway is that magic exists within the Marvel Cinematic Universe the same as science does in our universe. It is simply something that exists, and it is harnessed and utilized in various ways by various entities. Whether that utilization is through Thor's lightning powers or Wanda's telekinesis, magic in the MCU is, perhaps underwhelmingly, just an innate property of the universe. Humanity has always had this desire to ponder what we think is impossible, and yet as we advance those impossibilities become reality. Medicine, space travel, even things we take for granted every day like cell phones were once just ideas presented in our minds. Perhaps the same can be said about magic, and like with Stephen Strange, we just need enough time and practice to unlock those magical properties for ourselves.