Ai simple projectile shots

i just want to simply have a type of enemy that will shoot at you (like 1 shot for every 1/2 second)

(the game is in the y-axis, all the enemies are coming straight down at me.)

i appreciate all advice and hell Thanks :D

Take a look at this (poorly-named) 'delay question'. It shows how to implement a delay between shots. As for shooting, there are plenty of other questions about shooting, bullets and projectiles.

If you get stuck at any particular part, post the code you have so far and I'll happily try to step through it with you, but these links should set you on the right track.