Firstly, let me write down my code for you.
def AorB():
    with open('AB.txt', 'r+') as f:
        A = ['A', 'The Letter A']
        B = ['B', 'The Letter B']
        c = input('Write A or B >>>_ ')
        if c in A:
            print('You wrote A')
            add = input('Write Something Here! >>>_ ')
            f_contents = f.read()
            f.seek(0)
            f.write(add + '\n')
            more_line = input('Would you like to write more lines? >>>_ ')
            if more_line == 'Y' or 'y':
                AorB()
            if more_line == 'N' or 'n':
                print('You wrote No!')
AorB()
What the result is...
Write A or B >>>_ (Wrote A)
You wrote A
Write Something Here! >>>_ (Writes Something.)
Would you like to write more lines? >>>_ (Wrote N)
Write A or B >>>_ 
As you can see it looped back to the beginning. my desired result is
Write A or B >>>_ (Wrote A)
You wrote A
Write Something Here! >>>_ (Prints something.)
Would you like to write more lines? >>>_ (N)
You wrote No!
 
     
    