How do you make space invaders on scratch?

This set of instructions if for you controlled player

CONTROL: When green flag clicked, forever if (left key pressed) move -10 steps.

When green flag clicked, forever if (right key pressed) move 10 steps.

New Sprite, make a small bullet.

BULLET: When space pressed, go to (sprite 1/Control), Repeat 35 (change y by 10)

New sprite, Make your invader alien.

ALIEN: Go to (chosen coordinates), REPEAT UNTIL (y position = -130)

(move (amount of steps to end of screen) steps, change y by -15, move (amounts of steps to the start of screen))

duplicate the alien and change the coordinates for each one.