What does Microcontroller do when its powered on? Does the oscillator gives out clock signals and it executed instructions or what it does . I wish to know the flow . Can anybody help me ?

 

Given that the controller has some working clock source. It will start to execute instructions from the program memory. Are you interested in starting with microcontrollers. But unsure what to do

 

A microcontroller will go through a reset sequence, usually making all ports tri state and will set up some registers to initial values.
Once it is properly reset it will start executing its program.