In Metaphysics, Aristotle lays out his four causes as answers to "why" questions. In other words, if we were to ask why something is as it is, we would want to answer it with respect to the following four reasons:
1) The corporeal, or material reason/cause that something exists. This means: what is something made of. Aristotle gives an example of a bronze statue. The bronze is what the statue is made up of, and is the material cause for why the statue is as it is.
2) The shape, form, or formal reason/cause of why something is as it is. In the case of the bronze statue, its form, or its shape, is the formal reason for why the statue is as it is.
3) The functional, or efficient, reason/cause. This cause states that the reason why the statue takes the form that it does is because it underwent an entire process of having its bronze melted and poured into the mold of a statue. For Aristotle, it is not just that the artist made it that explains how the statue came to be, rather the artist knew how to make it and this knowledge is the ultimate functional, or efficient, cause of the statue.
4) The ultimate, or final, reason/cause that something is. Aristotle refers to this as "the end," which is "that for the sake of which a thing is done." In other words, we are now considering reasons; we are considering the reason why the statue exists or is as it is. One possible answer is that the bronze artisan wanted to create it that way. Another is that someone else wanted it that way. But for some things, Aristotle acknowledges that the final cause is an unanswerable mystery.
These four principles of causality are different from the ideas of being/becoming, or causality, that Plato sets out in his dialogue Timeaus. The biggest difference is that Plato is not as concerned with the process of causality as Aristotle is. In Timeaus, it satisfies him simply to state that anything that comes into being has a cause (28a4–6, c2–3). He also states that there are some things that exist, such as thoughts, ideas, or ideal forms, that will always exist, but never necessarily come into being (27d6). He further states that the universe is a visible, tangible thing that has come into being (28b7; from 5a–c, and 4).
Hence, while Aristotle uses cause to explain "why" questions, Plato uses being/becoming to explain the "why" questions without considering steps or processes.