I'll just give 2 examples. One with the every second condition & one using the on created condition:
I hope this helps:
Every Second Condition:
*Every (3) seconds...
->Create Object (Bullet) at Layer ("Layer"); at X = 0 ; Y = Player.Y ;
->Bullet -> Set angle of motion to 0.
---------------------------------------------
On created condition:
*On (Bullet) Created...
->Bullet -> Set Y to (Player.Y).
->Bullet -> Set angle of motion to 0.
On the every Second condition, replace the X with what you want.
The Every Second & On created condition are both triggers. That causes each bullet to only have the player's altitude at the moment the bullets are created/
at the moment the timer triggers