examples/basics/add_numbers.py
from __future__ import print_function

def main():
    a = raw_input('First number: ')
    b = raw_input('Second number: ')
    print(int(a) + int(b))

main()
First number: 2
Second number: 3
5

In order to convert the string to numbers use the int() or the float() functions. Whichever is appropriate in your situation.

How can I check if a string can be converted to a number?