Q:

I'm a beginner programmer, and I need to inquire about return statements

So I'm having some troubles with making a guessing game function that keeps score of how many times you get it correct. I currently have two problems:

The code causes the function to activate twice, is there any way to both print a function's returned value and assign a variable to it?
The variable "score" never goes beyond 1 because if the number you guess is wrong, the function returns none and goes back to 0

Here is my code, it's a mess:
def GuessingGame(score):

    rng = random.Random()
    numbertoguess = rng.randrange(1,10)
    guess = int(input ("What is your guess for a number between 1 and 10?"))
    if numbertoguess == guess:
        print ("Great guess! You're correct.")
        int (score = score + 1)
        return score
    else:
        print ("Wrong, the number was "+str(numbertoguess)+".")

playagain = "yes"

score = 0

while playagain == "yes":

    print ("The score is now "+str(GuessingGame(score))+".")
    score = GuessingGame(score)
    playagain = input ("Play again? (yes or no)")
    if playagain != "yes":
        print ("Goodbye")
    else:
        pass

A:

This line is actually calling the function:
print ("The score is now "+str(GuessingGame(score))+".")

You should just use:
print ("The score is now "+ str(score) +".")

score is a variable, and can be used as such
To answer the second question, you are not returning in the else: clause.
Instead of this:
if numbertoguess == guess:
    print ("Great guess! You're correct.")
    int (score = score + 1)
    return score
else:
    print ("Wrong, the number was "+str(numbertoguess)+".")

You could just return score in both cases like so:
if numbertoguess == guess:
    print ("Great guess! You're correct.")
    int (score = score + 1)
else:
    print ("Wrong, the number was "+str(numbertoguess)+".")
return score

Also, this line may not be doing what you want:
int (score = score + 1)

There's no reason to cast this, just use this line:
score = score + 1

Or:
score += 1

One final note is the GuessingGame would be better styled like:
guessing_game

According to PEP8

