This is a complicated cluster of interconnected, poorly-defined human-related notions, such as consciousness, self-awareness, mind, qualia, emotions etc. And there are a lot of theories, scientific and philosophical, trying to explain those concepts, but they are all have their shortcomings. The fact is, we don't have in this area anything similar to evolution theory in biology or general relativity + quantum mechanics in physics.
And it is even more complicated because those notions are tainted (often tacitly) by the religious idea of "soul".
In such state of affairs, it seems that the general question "what is ..." (consciousness, emotions, mind, and so on) is quite pointless. It should come in context, in other words, be complemented by a purpose of asking.
For example, people may be interested in consciousness (and the related concepts) for those reasons:
1. Technological, e.g. is it possible to transfer (upload) a human mind into the computer?
2. Moral-legal, e.g. at which stage turning off an AI will be considered as a murder?
3. Scientific, e.g. what exactly is the cause of the wave function collapse?
4. Exploratory, e.g. what are the possible altered states of consciousnesses, how to reach them and how to come back?
...and the list could be continued: education, medicine, warfare, psychology...