One of the big metaphysical concepts is consciousness. It's something we experience and are aware of directly. You know your own mind. You think, you feel, you focus, you remember, and you perceive. It's so immediate that some philosophers started with an awareness of their minds, and posited it as being primary. Reality you only know through your senses, but your mind! You know that first hand!
Let's try to narrow down the discussion a bit first. Consciousness is an awareness of reality. It's not a state, but a process. The process is one of perceiving the world, of identifying what you see, of analyzing what you know, etc. When you're aware of your mind, you're aware of it doing something. Whether it's solving a problem, or remembering something from you childhood, or examining something in a microscope, you are aware of the actions.
Awareness requires something to be aware of. Once you've begun the process of awareness, you can then focus on the actions that are involved in that awareness. But that's the second step. The first thing you need to do is be aware of something. In other words, you can become aware of your own awareness, but only after it exists. You have to initially be aware of something else.
Imagine you start from scratch. You have the potential of a mind, but there's no data to process. It sits inert. It's when outside information, i.e. reality, is presented to the mind that it starts actively perceiving it. The process has started only at this point. Before that point, the "mind" would be passive. It can't be aware of anything because there's nothing to be aware of, including itself. It's only when the mind starts actively processing the information that it can notice it's own actions, and focus on them.
This is the Objectivist reasoning for why a consciousness cannot exist without something to be conscious of. That view is expressed by having a god which is the creator of reality. This god is supposed to be some disembodied consciousness, and yet it has nothing to be conscious of. What could that even mean? What is the nature of such a thing? It has no data to analyze, no memories of data, no nothing. The answer, of course, is that god is beyond our understanding. Of course. Since he's impossible by our understanding, that's the only way to keep the dream alive.
So when we talk about a mind, we're really talking about the process. A mind doesn't exist in a physical way, as something you can point to. It's a process of awareness. The process can take many forms. It includes perception, remembering, abstracting, integrating, focusing, and every other mental function.
The forms of awareness can be different as well. A man sees the world in a different way than an animal, and I'm not talking about senses. A man integrates his knowledge, forms concepts, becomes aware of his own mental processes, and so much more. At the lower end of animal awareness you have little more than perception, and whatever it can retain in its head at the moment. Although the differences may be large, the fact of awareness is the same.