在使用config函数时，你必须提到你想改变什么。try：- answer_label.config(text="Text that you want to be displayed")
此外，您还没有从Entry小部件中获取值：为此，您可以用途：answer_label.config(text=main_entry.get())
完整的代码看起来像这样：

import tkinter as tk

root = tk.Tk()
root.attributes('-fullscreen', True)

exit_button = tk.Button(root, text="Exit", command = root.destroy)
exit_button.place(x=1506, y=0)

def answer():
    answer_label.config(text=main_entry.get())

frame = tk.Frame(root)
main_entry = tk.Entry(frame, width=100)
main_entry.grid(row=0, column=0)
go_button = tk.Button(frame, text='Go!', width=85, command = answer)
go_button.grid(row=1, column=0)
answer_label = tk.Label(text = "Hey")
answer_label.pack()
frame.place(relx=.5, rely=.5, anchor='center')

root.mainloop()

这个代码可以工作。它配置标签以更改文本。我不知道你想用config（main_entry）实现什么。

import tkinter as tk

root = tk.Tk()
root.attributes('-fullscreen', True)

exit_button = tk.Button(root, text="Exit", command = root.destroy)
exit_button.place(x=1506, y=0)

def answer():
    global main_entry, answer_label
    answer_label.config(text="hi")

frame = tk.Frame(root)
main_entry = tk.Entry(frame, width=100)
main_entry.grid(row=0, column=0)
go_button = tk.Button(frame, text='Go!', width=85, command = answer)
go_button.grid(row=1, column=0)
answer_label = tk.Label(text = "Hey")
answer_label.pack()
frame.place(relx=.5, rely=.5, anchor='center')

root.mainloop()