If anyone has any updates please do so :)

from tkinter import *
import os

creds = 'tempfile.temp'
def Signup():
    global pwordE
    global nameE
    global roots

    roots = Tk()
    roots.title('Signup')
    intruction = Label(roots, text='Please Enter new Credidentials\n')
    intruction.grid(row=0, column=0, sticky=E)
    r = Tk()
    r.title('Username Requirements')
    r.geometry('650x40')
    rlbl = Label(r, text='For the Username Please use the first three letters of your name and your age at the end. Example:Kamil...15...Kam15')
    rlbl.pack()
    r = Tk()
    r.title('Password Requirements')
    r.geometry('540x40')
    rlbl = Label(r, text='For the password use one uppercase. Two numbers and symbols. Thank you. Example:$am!elrf4')
    rlbl.pack()

    nameL = Label(roots, text='New Username: ')
    pwordL = Label(roots, text='New Password: ')
    nameL.grid(row=1, column=0, sticky=W)
    pwordL.grid(row=2, column=0, sticky=W)

    nameE = Entry(roots)
    pwordE = Entry(roots, show='*')
    nameE.grid(row=1, column=1)
    pwordE.grid(row=2, column=1)

    signupButton = Button(roots, text='Signup', command=FSSignup)
    signupButton.grid(columnspan=2, sticky=W)
    roots.mainloop()

def FSSignup():
    with open(creds, 'w') as f:
        f.write(nameE.get())
        f.write('\n')
        f.write(pwordE.get())
        f.close()

    roots.destroy()
    Login()


def Login():
    global nameEL
    global pwordEL
    global rootA

    rootA = Tk()
    rootA.title('Login')

    intruction = Label(rootA, text='Please Login\n')
    intruction.grid(sticky=E)

    nameL = Label(rootA, text='Username: ')
    pwordL = Label(rootA, text='Password: ')
    nameL.grid(row=1, sticky=W)
    pwordL.grid(row=2, sticky=W)

    nameEL = Entry(rootA)
    pwordEL = Entry(rootA, show='*')
    nameEL.grid(row=1, column=1)
    pwordEL.grid(row=2, column=1)

    loginB = Button(rootA, text='Login', command=CheckLogin)
    loginB.grid(columnspan=2, sticky=W)

    rmuser = Button(rootA, text='Delete User', fg='red', command=DelUser)
    rmuser.grid(columnspan=2, sticky=W)
    rootA.mainloop()

def Quiz():
    global nameEL
    global pwordEL
    global rootA
    r = Tk()
    r.title("Quiz")
    rlbl = Label(r,text='\n[+] Welcome user!')
    r.geometry('150x45')
    rlbl.pack()
    r = Tk()
    r.title("Quiz")
    rlbl = Label(r,text="This is a quiz about History and computing! Which one would you like to do first?")
    r.geometry('500x35')
    rlbl.pack()
    master = Tk()
    var1 = IntVar()
    HistoryL = Checkbutton(master, text="History", variable=var1).grid(row=0, sticky=W)
    var2 = IntVar()
    ComputingL = Checkbutton(master, text="Computing", variable=var2).grid(row=1, sticky=W)
    var1 = Button (rootA, text='History', fg='black', command=History)
    var1.grid(columnspan=2, sticky=W)
    var2 = Button (rootA, text='Computing', fg='black', command=Computing)
    var2.grid(columnspan=2, sticky=W)
    rootA.mainloop()

def History():
    global nameEL
    global pwordEL
    global rootA
    a = Tk()
    a.title("History")

def Computing():
    global nameEL
    global pwordEL
    global rootA
    b = Tk()
    b.title("Computing")

def CheckLogin():
    with open(creds) as f:
        data = f.readlines()
        uname = data[0].rstrip()
        pword = data[1].rstrip()

    if nameEL.get() == uname and pwordEL.get() == pword:
        r = Tk()
        r.title('Valid Details')
        r.geometry('150x50')
        rlbl = Label(r, text='\n[✔] Logged In')
        rlbl.pack()
        rmuser = Button(rootA, text='Next', fg='Blue', command=Quiz)
        rmuser.grid(columnspan=2, sticky=W)
        rootA.mainloop()
    else:
        r = Tk()
        r.title('Invalid Details')
        r.geometry('150x50')
        rlbl = Label(r, text='\n[❌] Invalid Login')
        rlbl.pack()
        r.mainloop()

def DelUser():
    os.remove(creds)
    rootA.destroy()
    Signup()

if os.path.isfile(creds):
    Login()
else:
    Signup()