What code should I use for moving asteroids in my pygame asteroids game?

Question

So I have a task to build a game and I decided to build a Shmup or a shoot em up, in which the spaceship has to survive for as long as it can whilst dodging asteroids. I have added the base of the game, such as the movement mechanics for the spaceship and borders but I need to add asteroids, but I am very inexperienced and am a total beginner(I did this just looking through guides), so I need some help to make the asteroid code in which the asteroids randomly generate outside the screen and then come on the screen towards the player. I thank you in ahead for spending time to answer my question.

Here is the code:-

import pygame
import random


from pygame.constants import SCRAP_SELECTION
WIDTH, HEIGHT = 300, 500
WIN = pygame.display.set_mode((WIDTH, HEIGHT)) # window
pygame.display.set_caption("Shmup")


#colours

WHITE = (255,255,255)
BLACK = (0, 0, 0)
RED = (255, 0, 0)



FPS = 60
VEL = 5
SPACESHIP_WIDTH , SPACESHIP_HEIGHT = 55,40

#imgs
YELLOW_SPACESHIP_IMAGE = pygame.image.load('spaceship_yellow.png')
YELLOW_SPACESHIP = pygame.transform.scale(YELLOW_SPACESHIP_IMAGE, (SPACESHIP_WIDTH, SPACESHIP_HEIGHT))
ASTEROID_IMAGES = pygame.image.load('asteroid.png')
ASTEROID = pygame.transform.scale(ASTEROID_IMAGES, (40, 40))

#movement
def movement(keys_pressed, yellow):
    keys_pressed = pygame.key.get_pressed()
    if keys_pressed[pygame.K_LEFT]:
            yellow.x -= VEL
    
    keys_pressed = pygame.key.get_pressed()
    if keys_pressed[pygame.K_RIGHT]:
        yellow.x += VEL
    
    keys_pressed = pygame.key.get_pressed()
    if keys_pressed[pygame.K_UP]:
        yellow.y -= VEL
    
    keys_pressed = pygame.key.get_pressed()
    if keys_pressed[pygame.K_DOWN]:
        yellow.y += VEL


#draw
def draw_window(yellow):
    WIN.fill(WHITE)
    WIN.blit(YELLOW_SPACESHIP, (yellow.x, yellow.y))
    pygame.display.update()




#main code
def main():
    yellow = pygame.Rect(50, 450, SPACESHIP_WIDTH , SPACESHIP_HEIGHT) #the spaceship is called yellow

    clock = pygame.time.Clock()
    run = True
    while run:
        clock.tick(FPS)
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                run = False

        if yellow.right > WIDTH:
            yellow.right = WIDTH
        if yellow.left < 0:
            yellow.left = 0

        if yellow.top < 0:
            yellow.top = 0
        if yellow.bottom > HEIGHT:
            yellow.bottom = HEIGHT





        keys_pressed = pygame.key.get_pressed()
        movement(keys_pressed, yellow)

    

        draw_window(yellow)
    
    pygame.quit()


if __name__ == "__main__":
    main()