函数second仅在脚本启动时执行一次。所以它不会将b更改为10。您可以将second函数的内容移动到first：

from tkinter import *
import time

def first():
    global a, b
    a += 1
    labelA['text'] = a
    if a == 3:
        b += 2
        labelB['text'] = b

    if b == 2:
        time.sleep(1)
        b = 10
        labelB['text'] = b

root = Tk()
root.geometry('500x500')
root.resizable(False, False)
a = 0
b = 0
labelA = Label(text=a)
labelA.pack()
labelB = Label(text=b)
labelB.pack()
button = Button(command=first, width=30, text='click to do something')
button.pack()
root.mainloop()

因为你只在程序开始时调用函数second一次。也许你可以在函数first的末尾添加second()。并将函数second中的语句b==10更正为b=10。

如果你想在一段时间后执行函数，你可以在Tkinter中使用root.after。修改后的功能将是：

def first():
    global a, b
    a+=1
    labelA["text"] = a
    if a==3:
        b+=2
        labelB["text"] = b
        #Call the second() function since 'b' is already equal to 2
        #This will call the second function after 1 second
        root.after(1000, second) #1000ms = 1s

    else:
        pass

def second():
    global b
   
    b = 10 #Don't put two equal signs here
    labelB["text"] = b

button = Button(command=first, width=30, text="click to do something")
button.pack()

请注意，我们在second后面不使用括号。

try this one code it working for me proper
import tkinter as tk

def my_function(event):
    print("Function started")

root = tk.Tk()

# Create a widget (e.g., a canvas) where you want to trigger the function.
canvas = tk.Canvas(root, width=200, height=100)
canvas.pack()

# Bind an event to the widget (e.g., <Button-1> for left mouse click).
canvas.bind("<Button-1>", my_function)

root.mainloop()