TypeError: unsupported operand type(s) for -: ‘str’ and ‘int’

The reason this is failing is because (Python 3) input returns a string. To convert it to an integer, use int(some_string).

You do not typically keep track of indices manually in Python. A better way to implement such a function would be

def cat_n_times(s, n):
    for i in range(n):
        print(s) 

text = input("What would you like the computer to repeat back to you: ")
num = int(input("How many times: ")) # Convert to an int immediately.

cat_n_times(text, num)

I changed your API above a bit. It seems to me that n should be the number of times and s should be the string.