I am a beginner in this field. I have read Special theory of relativity by Einstein, but the one written for beginners, not the technical. I have also read couple of undergraduate books which had STR. From my understanding, STR is a theory about transformation from one frame to another, both inertial. My question is, does all the notion of time and space being relative arise solely due to the fact that different observers traveling at different speeds perceiving events differently due to light reaching them at different times? Is light reaching observers differently the underlying idea of STR? I am confused. Or is it got to do with the fact that Space time curves at different relative speeds?..