import tkinter

def click_btn():
    txt = entry.get()
    button['text'] = txt

root = tkinter.Tk()
root.title('第一個文字輸入欄位')
root.geometry('400x200')
entry = tkinter.Entry(width = 20)
entry.place(x = 20, y = 20)
button = tkinter.Button(text = '取得字串', command = click_btn)
button.place(x = 20, y = 100)
root.mainloop()