You mean to say when does consciousness arise? - I suggest you read some Carl Jung, or some eastern philosophy.
Consciousness arises when one thinks about things. When one is pondering superficial ideas and the like. Sometimes great things happen when people think. But most of the time it is pretty selfcentered bullshit. I suggest you stay away from thought to be honest.
There are apparently different levels or modes of consciousness. Some people try to er.. Describe these layers/modes: Timothy Leary for one, and many other hallucinogenic users.
I think i've covered what it is: it is thought.
How do we know it? Simple we hear a little voice inside our head that tells us something. It dictates an idea you are thinking aloud in the hollow head we all have