Kant and Aristotle are quite different in their ethical systems, although both are approachable to the non-philosopher, or average person. I will get to Levinas later, as his philosophical system is not as easy to comprehend. Beginning with the more "modern" philosopher, Kant has a concept of morality described in Foundations of the Metaphysics of Morals. In this treatise, Kant explains that individual morality should rest upon making every decision by considering that what one does would become a universal law. Wondering if you should speed on what looks like an empty street? Kant would say you should not because if everyone sped, what would the consequences be? We would live in a more dangerous world. Kant's morality is somewhat similar to the kinds of laws we make to reduce the possibility that individual action can affect the group.

Aristotle had a much more free-flowing approach to life, in line with basic ancient Greek philosophy that said the three most important attributes are health, beauty, and wealth (honestly acquired). The Greeks recognized that some people had better lives than others, but all should live according to their best self. People should strive to optimize their happiness and express the best that is in them. This is to say that if you live your ideal life, living up to your potential, then you live an ethical life, which doesn't provide much guidance for most of us.

Levinas is more modern than Kant, and as an existential philosopher, he wrestles with more abstract concepts. His account of ethics rests in understanding that while everyone we encounter is an Other, our relationship to them and our actions toward them constitute all of our morality. This has its limits, since his morality is grounded in how we treat others but falls short in examining different types of relationships or relationships with other beings (such as animals, or Earth itself). Levinas also assumes our treatment of the Other is subjective and instinctual, but Levinas does define morality as utterly human, an important distinction (and arguably improvement) when comparing Levinas to Aristotle or Kant. Levinas loosely defines ethics as, essentially, compassion because although we realize our encounters are with the Other, we also treat them gently.

The three philosophers you mention lived centuries apart and lived in different parts of the world; as one might expect, there are significant differences in their ethical views and this can, at least in part, be attributed to the vast differences in their surroundings. Aristotle was a Greek philosopher from the 4th century BCE; Kant was a German philosopher from the 18th century; Levinas was a 20th century French philosopher. 

Aristotle's ethics are often described as "eudaimonistic;" this refers to the idea that he regards the best possible human life as consisting in eudaimonia ("flourishing" or "fulfillment" or "happiness"). His focus was on the right kind of life, and here, we already have the first difference with respect to Kant.

Kant, as was common among modern philosophers, focused on good acts rather than good lives. He argued that ethical actions require us to act in a dutiful manner in accordance with the moral law. A good human being is one who acts in accordance with the categorical imperative. 

These two conflicting approaches are often called agent-centered (Aristotle) and action-centered (Kant) ethics. 

Levinas' ethics falls completely outside this dichotomy and, indeed, is not an ethics in any traditional sense. His manner of conducting ethics was to offer a phenomenological account of precognitive interpersonal interaction. His work is almost metaethical in nature, unlike that of Kant or Aristotle.