How do i do this?

First question: are you wanting to do timed / elimination waves like Fruit Ninja? Or things appear when certain events occur (like become visible). I'll give you the appropriate answer after you answer that first question.

Thank you Ok awesome. 3D or 2D is not the only thing that decides whether you'll use Syncro Spawners or Triggered...Syncro Spawners are for when you have timed or elimination waves (like Galaga). Triggered Spawners allow more free-form design (spawn a wave when player hits this object for instance), but there is no elimination wave in triggered spawners.

So regardless of which way you go, you need to go to the LevelWaveSettings prefab in Project View and create one in your Scene by clicking the "Create LevelWaveSettings Prefab" button.
You should then go to its child prefab "Pool Boss" and check "Auto-add missing items" until later when you can set up pooling better.

Then you set up some Triggered spawners, which are just game objects in the Scene that you attach a Triggered Spawner component to.

Then you configure the Triggered Spawner to spawn a wave for certain events, like visible, or trigger enter. That should get you going. Watch the videos on youtube for a quick session of that.

Also, the example Scene #2 (Triggered Spawners) is a good one to study. The "Fighter 2" prefab has a triggered spawner that spawns laser shots at you on "visible" event.

Correct. You don't need to propagate events unless you're setting up "child spawners" like that mothership in the 3rd example video. It's not very common.

That warning is there so you don't wonder "where the heck are the propagate controls mentioned in the manual?"

wow!
I got it working!
thank you for this awesome asset it does just what I wanted it too!

you rock!

Ok cool! See my last reply a couple minutes ago. There's some more ideas for you there.