Recommended literature to learn essential aspects of signals and its propagation Where can I learn about signal's features. For instance mean, power, amplitude, frequency, energy,  how they propagate in space or any other medium?.


What power means its amplitude increases and decreases to draw the sine wave form through a bit of time. at stable value (forming logical message) depending on medium resistance and transmitting signal power, human code model frequently repeated (hi) started with character ends with another completed word (world) another word stared with a header and ends with trailer completed word.

out of electricity network that it out of control compared with communication signals networks even both of them propagate as a flood of electrons in cables, i need to know its shape in a medium, MW or Electromagnetic waves or in cables.
voice fades away at the moment you shot a word. you already carried it on a carrier to reach ear of who you talk to but at low power so that its power and frequency decreased and lose its shape at a point seems to be disappeared or absorbed to be converted to another shape of energy.

We carries it on a carrier varies depending on the medium converting carrier to cover all values voice reach as possible, more values means more quality. filtering the result to get carrier and voice met points.

just comments needed, books and papers.
It seems that you are looking for books to learn about multiple topics. Skimming through your question I think these are the topics:


Aspects of signals (signal mean, its power,amplitude,frequency,etc )
Signals propagation in space or any other medium


I would recommend parts of the following books :


Bernard Sklar - Digital Communications Fundamentals and
Applications 2nd Edition  
Bruce Carlson - Communications Systems 4th Edition  
Simmon Haykin - Communication Systems  4th Edition   
John G. Proakis - Digital Communications 4th Edition  


A little bit more deep:


D.G.Manolakis - Statistical and Adaptive Signal Processing - Spectral Estimation, Signal Modeling, Adaptive Filtering and Array Processing
Fuqin Xiong - Digital Modulation Techniques 2nd edition

edition