Hi Prafful,
in the example you’re referring to, we want to reverse a string:

word = input(‘Please enter a word:> ‘)
reverse_string = ”
for char in word:
reverse_string = reverse_string + char

print(reverse_string)

So, we iterate over each ‘char’ (or character) in the string and we append it backwards using reverse string. That’s why we need the order  char + reverse_string.
If we had reverse_string + char instead, we’d print back the exact same string we input, without reversing it.

In the future, could you please make sure to include a link to the lecture your question is about? It would make it a lot easier to answer the questions, especially since you’re naming your variables differently.

Best,
Eli