Hi,
you can do that i different ways but the basics are the same.
make an array, place the object (or prefabs) in it. use "Array Get" to select an object.
Then, depending on your needs you can use "Create Object" to create from a prefab (or duplicate from an object in the scene) OR you can have you objects already in place and use "Activate Game Object" to activate/deactivate your object OR you can move your objects from off screen.