You can use .place() for your label since your frame and your label have different parents. In place() you can use anchor="center" specify the startingpoint of your "anchor" with: x and y. Here is a working example:

app = Tk()
f = Frame(app,bg="yellow",width=50,height=50)
f.grid(row=0,column=0,sticky="NW")
f.grid_propagate(0)
f.update()
l = Label(f,text="123",bg="yellow")
l.place(x=25, y=25, anchor="center")
app.mainloop()

The problem is that you are reading the documentation for the tkinter label but you are using a ttk label. This is why you should not use wildcard imports -- when two modules export objects with the same name (eg: tkinter.Label and ttk.Label) it becomes difficult to know which one is being used in your code. The default for a ttk label is to be aligned left, but the tkinter label is aligned center, and the order of your imports means that you're using a ttk Label.

The quick fix for your example is to explicitly set the anchor option for the ttk label (eg: label.configure(anchor="center")).

You should also fix your imports so that this problem doesn't happen to you again. Instead of doing a wildcard import (eg: from tkinter import *) you should explicitly import the module as a unit, optionally with a shorter name. Once you do that, you need to prefix your widgets with the name of the module.

For example, given these import statements:

import tkinter as tk
from tkinter import ttk

... you would then create a ttk label with ttk.Label(...), and a tkinter label with tk.Label(...) which makes your code much easier to understand, and it removes all ambiguity.

In a line like

LabelTitle.place(x=x, y=y, anchor="center")

the anchor means to place the center of the label and the coordinates given by x and y.

Anyway, the thing is that Tk doesn't know how big the window is going to be until the main loop runs, so unless there's a flag to tell it to put the label there at that time (and there may be, I don't use Tk very often), you can't just set the position beforehand. I would do something like this:

def position_label(*args):
    LabelTitle.place(x=root.winfo_width() // 2, y=root.winfo_height() // 2, anchor='center')
root.bind("<FocusIn>", position_label)

So the root window gets focus after its geometry has been asserted, so we hook in a callback (position_label) to position the label at that time.

In my opinion, you should have used place or grid instead of pack. Because pack only gives few alignment options.

otherwise, maybe divide the main window into two frames then pack the label at the top of the lower frame

frame = Frame(root)
frame.pack()

bottomframe = Frame(root)
bottomframe.pack( side = BOTTOM )


L = Label(root, text="Welcome to 3P Connect 4!!!",font=("Ariel",20,"bold", "underline"))
L.pack(side = TOP)

I wish this helps. but you should use grid for better alignment or place.

Use the place geometry manager. Here is a simple example :

from tkinter import *

wd = Tk()
wd.config(height=500, width=500)
can = Canvas(wd, bg = 'red', height=100, width=100)
can.place(relx=0.5, rely=0.5, anchor=CENTER)

Basically the options work as follows:

With anchor you specify which point of the widget you are referring to and with the two others you specify the location of that point. Just for example and to get a better understanding of it, let's say you'd be sure that the window is always 500*500 and the widget 100*100, then you could also write (it's stupid to write it that way but just for the sake of explanation) :

from tkinter import *

wd = Tk()
wd.config(height=500, width=500)
can = Canvas(wd, bg = 'red', height=100, width=100)
can.place(x=200, y=200, anchor=NW)

relx and rely give a position relative to the window (from 0 to 1) : 0,4*500 = 200
x and y give absolute positions : 200
anchor=NW makes the offset options refer to the upper left corner of the widget

You can find out more over here :

http://effbot.org/tkinterbook/place.htm

And over here :

http://www.tutorialspoint.com/python/tk_place.htm

In the case of placing a single widget in the center of another widget, place is the best choice. It has options to locate a widget relative to another widget (usually, but not necessarily, relative to its parent).

In your case, you want the center of the label in the center of its parent. You can use a relative X coordinate of .5, a relative Y coordinate of .5, and an anchor of "center", meaning that the center of the widget is placed at the given coordinates.

Example:

nameLabel.place(relx=.5, rely=.5, anchor="center")