(Updated answer for fstrings) For big string like what you have do a few things.

First use """ """ instead of trying to build it the way you are.

You should then use preferably fstrings (Python 3.6+)

return f"""The GC content for non retained introns is {avg_gc(nr)}
The GC content for retained introns is {avg_gc(r)}
The average length of non retained introns is {intlength(nr)}
The average length of retained introns is {intlength(r)}
The percent of non retained introns divisible by 3 is {intdiv(nr)}
The percent of retained introns divisible by 3 is {intdiv(r)}.
"""

Older versions of Python can use:

return """The GC content for non retained introns is {nr_gc}
The GC content for retained introns is {r_gc}
The average length of non retained introns is {nr_avglen}
The average length of retained introns is {r_avglen}
The percent of non retained introns divisible by 3 is {nr_percdiv}
The percent of retained introns divisible by 3 is {r_percdiv}.
""".format(r_gc = avg_gc(r),
           nr_gc = avg_gc(nr),
           r_avglen = intlength(r),
           nr_avglen = intlength(nr),
           r_percdiv = intdiv(r)
           nr_percdiv = intdiv(nr))

You define a function with a parameter s. That function immediately throws that value away and asks for input. You are calling a function with the same name as that parameter, and sending it an argument of the function name. That doesn't make any sense.

def addExclamation(s):
    new_string = s + "!"
    return new_string

print(addExclamation('Hello'))

Or:

def addExclamation():
    s = input("please enter a string")
    new_string = s + "!"
    return new_string

print(addExclamation())

The and keyword is a boolean operator, which means it compares two values, and returns one of the values. I think you want to return a tuple instead, like this:

...
return (a, b)

And then you can access the values using the indexing operator like this:

a = lsubstr( ... )
a[0]
a[1]

Or:

word1, word2 = lsubstr( ... )

A few things:

1. Python spacing matters, so don't forget to indent!
2. Check your print syntax. Everything you're printing should be inside the parens

One form of correct syntax would be:

def fnc2(a, b, c):
    total = (a + b) * c
    print("The result is: " + str(total))