How does the code work [I for i in Range (51) if I % 2 == 0]?

  Evens_to_50 = [I  for  i  in   range  ( 51 )  if  i %  2  ==  0 ]   Print  Evens_to_50    
 This code generates a list of even numbers up to fifty. But I, as new in programming, do not understand some points -: 
  
  
 Why the generation occurs in square brackets, they are usually used when working with indices 
  
 What does the first  i  do  for ? Why after  range (51)  there are no colonies and transfer to a new line with tabulation? 
  
 Where else can square brackets use?  for  write? What are the rules in them?