Understanding Z transform

Hi All,

I was studying Z transforms and found pretty good material on the net, though I feel i do not have a proper understanding of the concept, could someone help me clear this.
I know that we apply z transforms for sequences and convert them to Z domain and find the values of z for which we get zeros and poles and also find the region of convergence, what I dint get is, why are we multiplying some z values to the given sequence and finding for what values of z the result gets pretty huge or dampens out. What does poles and zeros have to do with the given sequence, its not like we are applying the transform to a system and finding the system's response, its just a sequence.
And they also say that its a frequency domain transformation, how do we realise frequency here.

Thanks in advance,
NK