Call to website & blog owners,what are impressions, impressions/clicks & eCPM?

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In the process of monetizing my blog, i have applied for chitika one month back. But i have zero earnings in my account.I just don't understand the funda of impressions and impressions/click.I have peeped into my chitika earning report and found the number of impressions so far as 190.What does that mean and the column next,"impressions/click" shows "***" in it.When will i start earning?Is chitika a slow process.Please help me.