I want to completely understand how EFI works. Moreover, how and in what form it receives the message from the accelerator pedal. I specifically want to learn how it is implemented in Honda sedans like Civic and City AT versions.
EFI works by measuring the air flow. The accelerator pedal is directly connected to the throttle valve on old cars and indirectly (via an electrical connection) on new cars. There is a separate air mass flow meter (typically hot wire) that measures the mass of incoming air. When the mass flow is known, the EFI can using open loop control adjust the amount of fuel injected to match the amount of airflow.
There is also a second control system, the closed loop lambda control. The lambda sensor measures the oxygen levels in the exhaust, and the closed loop control maintains the oxygen level at near zero to result in complete burn with no residual oxygen. The reason for this closed loop control is that the catalytic converter works the best with stoichiometric air/fuel ratio.
All of this is done digitally using computers. The injectors are either closed or open, never partially open, and the amount of open duration is digitally controlled.
I'm pretty sure you could have found all of that on Wikipedia article about fuel injection already.