How can I create an input that will loop and create a new list each time?

You will need to create a variable which can store multiple contacts inside of it. Each contact will be a list (or a tuple. Here I have used a tuple, but it doesn't matter much either way).

For this you could use a list of lists, but a dictionary will be more suitable in this case.

What is a dictionary?

A dictionary is just like a list, except that you can give each of the elements a name. This name is called a "key", and it will most commonly be a string. This is perfect for this use case, as we want to be able to store the name of each contact.

Each value within the dictionary can be whatever you want - in this case, it will be storing a list/tuple containing information about a user.

To create a dictionary, you use curly brackets:

empty_dictionary = {}
dictionary_with_stuff_in_it = {
    "key1": "value1",
    "key2": "value2"
}

To get an item from a dictionary, you index it with square brackets, putting a key inside the square brackets:

print(dictionary_with_stuff_in_it["key1"])  # Prints "value1"

You can also set an item / add a new item to a dictionary like so:

empty_dictionary["a"] = 1
print(empty_dictionary["a"])  # Prints 1

How to use a dictionary here

At the start of the code, you should create an empty dictionary, then as input is received, you should add to the dictionary.

Here is the code I made, in which I have used a while loop to continue receiving input until the user wants to exit:

contacts = {}

msg  = "Would you like to: \n - n: Enter a new contact \n - g: Get details for an existing contact \n - e: Exit \nPlease type n, g, or e: \n"
action = input(msg)
while action != "e":
    if action == "n":  # Enter a new contact
        name = input("Enter name here: ")
        number = input("Enter phone number here: ")
        city = input("Enter city here: ")
        contacts[name] = (number, city)
        print("Contact saved! \n")
        action = input(msg)
    elif action == "g":  # Get details for an existing contact
        name = input("Enter name here: ")
        try:
            number, city = contacts[name]  # Get that contact's information from the dictionary, and store it into the number and city variables
            print("Number:", number)
            print("City:", city)
            print()
        except KeyError:  # If the contact does not exist, a KeyError will be raised
            print("Could not find a contact with that name. \n")
        action = input(msg)
    else:
        action = input("Oops, you did not enter a valid action. Please type n, g, or e: ")

#can be easier to use with a dictionary
#but its just basic
#main list storing all the contacts
Contact=[]

#takes length of contact list,'int' just change input from string to integer 
contact_lenght=int(input('enter lenght for contact'))

print("enter contacts:-")

#using for loop to add contacts
for i in range(0,len(contact_lenght)):
    #contact no.
    print("contact",i+1)

    Name=input('enter name:')
    Number=input('enter number:')
    City=input("enter city:")

    #adding contact to contact list using .append(obj)
    Contact.append((Name,Number,City))

#we can directly take input from user using input()
bck=input("Thank you! \nWould you like me to read your details back to you?[y/n]:")

#checking if user wants to read back
if bck=='y':
    u=input("enter your name:")

    #using for loop to read contacts
    for i in range(0,len(Contact)):

        #if user name is same as contact name then print contact details
        if u==Contact[i][0]:
            print("your number is",Contact[i][1])
            print("your city is",Contact[i][2])

else:

    #if user doesnt want to read back then print thank you
    print("Good bye")

For this purpose you should use a dictionary. The key of every entry should be the string 'User[0]' that corresponds to the person's name. The contents of every entry should be the list with the information of that user.

I'll give you an example:

# first we need to create an empty dictionary
data = {}

# in your code when you want to store information into
# the dictionary you should do like this
user_name = User[0] # this is a string
data[user_name] = User # the list with the information

If you want to access the information of one person you should do like this:

# user_you_want string with user name you want the information
data[user_you_want]

Also you can remove information with this command:

del data[user_you_want_to_delete]

You can get more information on dictionaries here: https://docs.python.org/3/tutorial/datastructures.html#dictionaries

You should start by defining a class to support name, phone and city. Once you've done that, everything else is easy.

class Data:
    def __init__(self, name, city, phone):
        self.name = name
        self.city = city
        self.phone = phone
    def __eq__(self, other):
        if isinstance(other, str):
            return self.name == other
        if isinstance(name, type(self)):
            return self.name == other.name and self.city == other.city and self.phone == other.phone
        return False
    def __str__(self):
        return f'Name={self.name}, City={self.city}, Phone={self.phone}'

DataList = []

while (name := input('Name (return to finish): ')):
    city = input('City: ')
    phone = input('Phone: ')
    DataList.append(Data(name, city, phone))

while (name := input('Enter name to search (return to finish): ')):
    try:
        print(DataList[DataList.index(name)])
    except ValueError:
        print('Not found')