Counter clicker

I got some code for my counter from someone, it is working console prints out 1 2 3 4... but I dont know how to make a label, that shows the value and i need to store it somewhere like
a = //That value//
so I can later use it in my shop like if a is = 20 he can buy something that will change how much points he gets, so like if a = 20 he buys that and now the score is like this 2 4 6.... and global value of the counter so if I change the value to 3 the counter will count like this 3 6 9....So I ask if someone here can help me make simple counter/adder to label and store the value globaly so i can refer to it anywhere, if it is possible I dont understand __init__ and self., so if someone can do it without it, it would be really great, but i can do with __init__ but for me it is very hard i am learing python and still i dont know what that is, even if I look on multiple sites that explained it, still I dont know.
Here is the counter but I dont know how to get the value global and refer to it anywhere.

import tkinter as tk

class Counter(object):

    def __init__(self, start: int = 0):

        self.value = start

    def add(self) -> int:

        if self.value < 900:

            self.value += 1

        print(self.value)

        return self.value

clicks = Counter()

root = tk.Tk()

tk.Button(root, text="click me!", command=clicks.add).pack()

root.mainloop()