Conscious is one of the great mysteries of psychologies, and it is difficult even to define the term. Most people understand what they mean by consciousness, as they are intuitively aware of their own.
In the most basic sense, consciousness is a state of awareness of one's own existence, sensations, and mental operations - and is most easily apprehended in comparison to its opposite, unconsciousness, which describes a state of complete unawareness. But this definition is a tautology, as consciousness and awareness are largely synonymous.
To be conscious is to be conscious of something. We are aware of things outside of the self because they stimulate the nerves of our sensory organs. We have somatic awareness by means of the nerves that are directly connected to our tissues and organs. The means by which we are aware of our thoughts is by means of attention to a stream of consciousness that is largely believed to be an internal dialogue - though we may also be conscious of thoughts that we are unable to describe in words, adequately or at all.
It is a common error to suppose we have direct consciousness of objects. All that is possible for us to be conscious of is the sensory stimulation they provide. That is, we are not conscious of an object that we encounter. We may see a but what enters into our mind is merely the optical sensations we experience: the optic nerves send perception to centers of the brain which process them, recognizing the object and its visual properties, and pass that information to the brain. If our perception and recognition are imperfect, we receive imperfect information, which is not the true nature of that which we have perceived.
Our consciousness even of our own bodies works in the same way: the stimulation is internal rather than external - the method by which the raw information is perceived is through different nerves, but it is still sensed and then interpreted, and any flaws in perception and interpretation cause us to perceive something as other than it truly is.
Also, we can state that we are only conscious of those things that the mind is experiencing of the moment - when we recall an experience of the past, we are not perceiving it presently and memory may further distort the information we have perceived, recombining and rearranging elements of experience.
It must not be thought that everything that is perceived is within the realm of consciousness - to do so is a misleading error, and all the worse for being completely unsupported by evidence of any kind, yet which still seems to persist.
In any given moment, all our senses are barraged by a great many thing. A walk down any busy street accosts us with a chaos of sights, sounds, scents, and tactile sensations - not to mention the somatic sensations of our own bodies and the prattle of our minds. Most of what we perceive is ignored by the conscious mind, which tends to work on only a few things at any given time.
There is a suggestion that everything we perceive is within our awareness, but this has never been sufficiently demonstrated. There may be things of which we are vaguely aware, but cannot recall even moments later - whether it is because they are ineffable or because our consciousness of the present moment overshadows that of the recent past, even seconds ago.
There is some evidence that we can recall different details at different times, and things that we do not believe that we were aware of come to mind, though there is the counter-argument that these details may be embellishments or confabulations created by the mind to fill gaps in our memory of a given moment.
The process by which we are aware of things without registering them in the conscious mind is called "the subconscious." We are often inordinately impressed by the seeming creativity or genius that we perceive when we later process or retrieve information that came to our awareness but not our attention. Just as we are impressed buy other people when they tell is something we did not know, so are we impressed with our own minds when they produce information we did not realize we had received.
It is therefore believed that the subconscious plane is where imagination does much of its work - again, because we were not attentive to the information or the thought process, it seems novel to us when it comes to our direct awareness.
As such, the field of psychology in the author's time gave rather too much attention to the subconscious mind, considering it to be a thing unto itself and the source of almost mystical powers.
That is not to dismiss the subconscious as unimportant, but merely to cast it in the proper perspective: the only difference between the subconscious mind and the conscious one is that we are not immediately attentive to it - such that it seems to magically appear when it comes to our attention. And "magic" is a fair analogy, in that many of the qualities ascribed to the subconscious mind are fantasies based on illusions and "tricks" of misdirected attention.