Difference between "from...import" and "import"

Just wondering what s the difference between from ‘a’ import ‘b’ and import ‘a’.

from string import lower
import pandas as pd

When you type just import you are importing the whole module, and for use a specific function from it you have to specify the name of the module before the function.
for instance:

import math
math.sqrt(16) #return 4

otherwise you can import the single function from it and omit the name of the module when you call it

from math import sqrt
sqrt(16) #return 4