If - Else

If

a = 33 
b = 200 
if b > a: 
  print("b is greater than a") 

An If statement, without indentation (will raise an error):

Else

The else keyword catches anything which isn't caught by the preceding conditions.

a = 200 
b = 33 
if b > a: 
  print("b is greater than a") 
else: 
  print("b is not greater than a") 

Elif

The elif keyword is Python's way of saying "if the previous conditions were not true, then try this condition".

a = 33 
b = 33 
if b > a: 
  print("b is greater than a") 
elif a == b: 
  print("a and b are equal") 

In this example a is equal to b, so the first condition is not true, but the elif condition is true, so we print to screen that "a and b are equal".

a = 200 
b = 33 
if b > a: 
  print("b is greater than a") 
elif a == b: 
  print("a and b are equal") 
else: 
  print("a is greater than b") 

In this example a is greater than b, so the first condition is not true, also the elif condition is not true, so we go to the else condition and print to screen that "a is greater than b".