What is impulse response (or equivalently the frequency response) of the channel ? Please allow me to ask this silly question. I googled, but I still not clear about this. What is impulse response of a channel (wireless communication channel). Someone can explain me with a lot of pictures? I know this question is too ez, but I really need to understand it fully. Thank you again.
This is a fundamental topic and it needs a lot of explaination.
I suggest you use the fading channel object of MATLAB, especially the Channel Visualization Tool.

There are lots of examples with visualization in this link. MATLAB channel OBJECT