Converting numbers to words - Python
This is good work! Well done as a beginner programmer. 


def changeNumberIntoLetter(value):
    number=numToLetter(value)
    return number



This function doesn't really do anything useful to be honest. Can't you directly use numToLetter.


if value==1: return 'one'
elif value==2: return 'two'
elif value==3: return 'three'
elif value==4: return 'four'
elif value==5: return 'five'
elif value==6: return 'six'



Instead of creating lot of if statements. Try using a dictionary like this:

NUM_TO_WORD_MAPPING = {1: "one", 2: "two"}


and you can refer the string to number using 

if value in NUM_TO_WORD_MAPPING:
    return NUM_TO_WORD_MAPPING[value]
else:
    # ... special cases.


As sergiy-kolodyazhnyy said, you can also use a list or a tuple. 


int(str(value)[-1])



use value % 10 to extract numbers easily. This is modulo operator and returns remainder after division. 



Bonus Content: Code Style

How your code looks like is as equally important as how you implement it. Because you and other programmers will spend time reading it.


  “Indeed, the ratio of time spent reading versus writing is well over
  10 to 1. We are constantly reading old code as part of the effort to
  write new code. ...[Therefore,] making it easy to read makes it easier
  to write.”
  
  ― Robert C. Martin, Clean Code: A Handbook of Agile Software
  Craftsmanship


Let's take a look at your function


def numToLetter(value): #The function converts the numbers into letters. 



I recommend that you use snake_case (number_to_letter) as it is considered industry standard for python programs. Comments are better done using """ comment """ style.

In this scenario however comment is not really required because your function name says that it's purpose is converting number to letter. People usually forget to update comments and it ends up giving incorrect information. If you want to use documentation comments anyway, make sure that comments are always up to date.

Reading material:


PEP-8 - Coding conventions / standard
PEP-287 - Document comment standard
Documentation related SO Question