Using encryption/hashing to create a secure login I am creating a login for an encrypted chat application which retrieves login information from a MySQL database. I have got to the point where I feel pretty confident that (to the best of my knowledge) it is relatively secure. I am trying to learn so feel free to criticize!

import hashlib
import mysql.connector
from tkinter import *
from tkinter import messagebox
from cryptography.fernet import Fernet

chat = Tk() #Api I am using to create the GUI for the application

#Connect to MySQL database
try:
    loginFRetrieve = open("LK.bin", "rb") #Retrieving Encryption key from file
    retrivedKey =  loginFRetrieve.read()
    loginFRetrieve.close()

    loginFRetrieve = open("LC.bin", "rb") #Retrieving MySQL server login credentials
    retrivedLC = loginFRetrieve.read()
    loginFRetrieve.close()

    cipher = Fernet(retrivedKey)
    retrivedLC = cipher.decrypt(retrivedLC) #Decrypting server login data from file
    retrivedLC = retrivedLC.decode('utf-8')
    lC = retrivedLC.split()

    mydb = mysql.connector.connect(host=lC[0],user=lC[1],passwd=lC[2],database=lC[3])
    del(lC)
except mysql.connector.Error as err:
    chat.withdraw()
    messagebox.showerror("Database Error", "Failed to connect to database")
    exit()



mycursor = mydb.cursor()

#hashPass hashes and returns a string of characters using SHA-256 algorithm
def hashPass(hP):
    shaSignature = \
        hashlib.sha256(hP.encode()).hexdigest()
    return shaSignature

#userExists checks a database too see if username exists in the database
def userExists(userName):
    mycursor.execute("SELECT username FROM logins WHERE username = '%s'" % userName)
    userResult = mycursor.fetchall()
    if userResult:
        return True
    return False

#Creates a new user in the connected SQL database.
def newUser(nU, nP):
    if userExists(nU) == False:
        mycursor.execute("SELECT username FROM logins WHERE username = '%s'" % nU)
        mycursor.fetchall()
        r = hashPass(nP)
        sql = "INSERT INTO logins(username, passwordhash) VALUES(%s,%s)"
        val = (nU, r)
        mycursor.execute(sql, val)
        mydb.commit()
        chat.title(string="User created")
    else:
        messagebox.showwarning("User Creation Error", "User already exists")

#Checks the connected SQL database for an existing user.
def existingUser(uN, pW):
    if userN.get() != "":
        if userExists(uN) == True:
            encryptedPass = hashPass(pW)
            mycursor.execute("SELECT * FROM logins")
            passResult = mycursor.fetchall()
            for row in passResult:
                if row[1] == uN and row[2] == encryptedPass:
                    chat.title(string="Login Successful!")
                elif row[1] == uN and row[2] != encryptedPass:
                    messagebox.showerror("Login Error", "Password does not match our records")
        else:
            messagebox.showerror("Login Error", "User does not exist")
    else:
        messagebox.showwarning("Login Error", "Please enter a username")
Encryption isn't Hashing
encryptedPass = hashPass(pW)

You're not encrypting the password, you're hashing it.
For passwords you should not be hashing them with the SHA2 family. Instead, use bcrypt.
Sanitize input
From my limited knowledge of Python, it doesn't appear you're sanitizing your input on some functions, for example userExists() and the first query in newUser(). Instead, you're using simple string formatting to substitute values directly.
You should be passing the variables as arguments to execute() every time.