This is a simple one:

while True:
    a = input("Enter yes/no to continue")
    if a=="yes":
        gameplay()
        continue
    elif a=="no":
        break
    else:
        print("Enter either yes/no")

Where gameplay function contains the code to be executed

(I'm going to try not to give you the answer, but to push you towards it)

You want the while loop to run over and over again until the user inputs neither yes or no, right? So you'd want to break out of the loop if the answer is yes, break out of the loop if the answer is no, else try again, so you need to set up the condition for exit, for entry, and the logic in between.

As for where you'd put the while loop, you want to put it on the global line, then all your logic indented inside.

You are first calling yes_or_no, which outputs a value but you throw it away and are calling the function again instead of testing on the output of the first call.

Try storing the output in a variable.

# Store the output in a variable
answer = yes_or_no()

# Conditional on the stored value
if answer == 1:
    print("You said yeah!")

else:
    print("You said nah!")

Side notes

It is considered bad practice to use capitalized names for variables, those should be reserved for classes.

Also, a user-prompt loop is better implemented with a while-loop to avoid adding a frame to your call-stack every time the user enters a wrong input. This is unless you use an interpreter which implements tail-call optimization, which cPython does not.

Here is what an improved version of your function could look like.

def yes_or_no():
    while True:
        answer =  input("Yes or No?").lower()

        if answer == "yes":
            return 1

        elif answer == "no":
            return 0

Try:

def yes_or_no(question):
    reply = str(input(question+' (y/n): ')).lower().strip()
    if reply[0] == 'y':
        return 1
    elif reply[0] == 'n':
        return 0
    else:
        return yes_or_no("Please Enter (y/n) ")

print("started")
while True:
    # DRAW PLOT HERE;
    print("See plot....")
    if(yes_or_no('Do you like the plot')):
        break
print("done")

Best to keep function definition separate from loop for clarity. Also, otherwise it will be read in every loop wasting resources.

Output:

$ python ynquestion.py 
started
See plot....
Do you like the plot (y/n): n
See plot....
Do you like the plot (y/n): N 
See plot....
Do you like the plot (y/n): NO
See plot....
Do you like the plot (y/n): No
See plot....
Do you like the plot (y/n): no
See plot....
Do you like the plot (y/n): yes
done
$

//This code is for explanation 

quiz = str(input("would you like to answer some questions \n choose y/n"))

quiz = quiz.lower()

while quiz != 'y' and quiz != 'n': //here you are using != that will result false this logic works fine with !

//while quiz == 'y' or quiz == 'n': //will work for or

print("please choose 'y' or 'n'")

input("y/n?")

//this code will work 

quiz = str(input("would you like to answer some questions \n choose y/n"))

quiz = quiz.lower()

while quiz != 'y' and quiz != 'n':

   print("please choose 'y' or 'n'")

   input("y/n?")

I hope this helps.

You may be interested in flow charts or Algorithms please follow this link: https://www.edrawsoft.com/explain-algorithm-flowchart.php

You may also be interested to learn about python more please follow this link: https://www.python.org/about/gettingstarted/

Thank you.