from tkinter import *

def clicked():
    res = 'Привет {}'.format(txt.get())
    lbl.configure(text=res)


window = Tk()
window.title('Добро пожаложенине в приложение  PythonRu')
window.geometry('400x250')
lbl = Label(window,text='Привет', font=('Arial Bold', 50))
lbl.grid(column=0, row=0)
txt = Entry(window, width=10)
txt.grid(column=1, row=0)
btn = Button(window, text='Клик', bg='black', fg='red', command=clicked)
btn.grid(column=2, row=0)
window.mainloop()