Meta-cognition is 'knowing about knowing'. When a person knows what strategies their mind is using, or knows what they are thinking or how they are thinking - then they are thinking about their own thinking - and that is 'meta-cognition'.
Nelson and Narens (1990) proposed a conceptual framework that has been adopted by most researchers. According to them, cognitive processes may be divided into those that occur at the object level and those that occur at the meta-level: The object level includes the basic operations traditionally subsumed under the rubric of information processing – encoding, rehearsing, retrieving, and so on. The meta-level is assumed to oversee object-level operations (monitoring) and return signals to regulate them actively in a top-down fashion (control). The object-level, in contrast, has no control over the meta-level and no access to it.
So the object level does the automatic processes that are directed or monitored by the conscious mind. For example - text-processing is automatic and therefore it is at the object or unconscious level - however (obviously) the text is also understood consciously. This is because there is a difference between what someone understands unconsciously and what someone is understanding consciously.
Everything the mind does without conscious awareness is by definition unconscious. Therefore, most of the mind and its functions are unconscious. For instance you may remember many things you don't know about - or even understand many things you don't know consciously (but at times that knowledge might rise to consciousness).