Draw a square in Python Turtle

I am following a tutorial for Python learning and I can't get the screen to open to draw. I don't get an error, it just shows that the program finish running. Maybe I missed something, can someone point it out?

 import turtle #acutally called turtle to draw a turtle beautiful also used 
to draw other stuff

 # to draw a square or eventually a turtle you need to do this things below
  # to draw a square you want to : move forward,turn right,move forward,turn 
 right,move forward turn right
def draw_square(): #draw square for turtles
    window = turtle.Screen() #this is the background where the turtle will 
  move
window.bgcolor("red") # the color of the screen
brad = turtle.Turtle() #this is how to start drawing like time.sleep you use turtle.Turtle
brad.forward(100)#move turtle forward takes in a number which is the distance to move forward
brad.forward(90)# moves right 
brad.forward(100)
brad.forward(90)
brad.forward(100)
brad.forward(90)
brad.forward(100)
brad.forward(90)
window.exitonclick() #click the screen to close it
draw_square()

Your primary error is these two lines are in the wrong order:

window.exitonclick() #click the screen to close it
draw_square()

The exitonclick(), or mainloop(), or done() should be the last thing your turtle code does as they turn control over to Tk's event loop. A rework of your code for the above and style issues:

import turtle

# to draw a square, or eventually a turtle, you need to do the things below

def draw_square():
    """ draw square for turtles """

    # to draw a square you want to : move forward, turn right,
    #  move forward, turn right,move forward turn right

    brad = turtle.Turtle()
    brad.forward(100)  # forward takes a number which is the distance to move
    brad.right(90)  # turn right
    brad.forward(100)
    brad.right(90)
    brad.forward(100)
    brad.right(90)
    brad.forward(100)
    brad.right(90)

window = turtle.Screen()
# this is the background where the turtle will move
window.bgcolor("red") # the color of the window

draw_square()

window.exitonclick()  # click the screen to close it