1 - Add a button to your layout. Place it where you would like it to appear. In your event sheet add an event that says "on clicked" -> "go to layout"
2 - Add a sprite and give it the bullet behaviour, in the event sheet add "Every tick" -> "Set bullet motion towards (object)"
3 - Add another event "On sprite destroyed" -> "System create particle effect at (Position of object"
I would strongly recommend you have a good read through some of the tutorials, practice a few, get to grips with construct and how each behaviour works and the options that go with it.
If all else fails, ask here in the forums, someone will assist where possible