I am getting indentation in this basic code in Python can someone explain this ?

In Python indentation is significant: identically indented lines of code form a block of code which is executed together.
So when you do an if ... else statement, all teh lines that are executed when the condition is true must share teh same indentation:

if condition:
   line 1
   line 2
else:
   line 3
   line 4
line 5

If the condition is true, both line 1 and line 2 will be executed, if it isn't, then both line3 and line 4 will be executed.

Your code has a second indented block in the middle:

if condition:
   line 1
   line 2
line 5
else:
   line 3
   line 4
line 5

Which means that the system cannot work out what the else code is doing there as the if statement was ended by line 5

(This is one of the stupid things about Python, and which causes the most problems: because any whitespace is taken as significant it is possible to have two adjacent lines of code that look identical but are differently indented because spaces and tabs are not the same. Make sure you use an editor that replaces tabs with spaces or it can get very, very confusing.)

Complex math takes care of the discriminant sign, so you may write

import cmath
sol1 = (-b-cmath.sqrt(d))/(2*a)
sol2 = (-b+cmath.sqrt(d))/(2*a)
print('The Solutions are {0} and {1}'.format(sol1, sol2))

Using the traditional ('real' math) approach:

import math
a = 1
b = -2
c = 4

# calculate the discriminant
d = (b**2) - (4*a*c)
if d > 0:
     sol1 = (-b-math.sqrt(d))/(2*a)
     sol2 = (-b+math.sqrt(d))/(2*a)
     print('The solutions are {0} and {1}'.format(sol1,sol2))
elif d == 0:
     sol12 = -b/(2*a)
     print('The solutions are {0}, one and the same'.format(sol12))
else:
     # here  d <0
     rp = -b/(2*a)
     ip = math.sqrt(-d)/(2*a)
     print('The Solutions are {0}+{1}j and {0}-{1}j'.format(rp,ip))