Your description is vague, I don't understand how the Gun-bullet-target mechanics should work. Is it like an angry birds clone or something?
It's a good practice to be more specific when you ask for help. Example capx and pictures help a lot to clarify an inquiry.
Why don't you try some of the templates that come with Construct 2? You can learn a lot by reverse engineering those examples. Also, be sure to try some of the tutorials found on the tutorial section of this site. If you can describe/fit your game with a game genre, search with some useful key words and you might find a relative tutorial.
What you ask now is for someone to build your game for you. At least be more specific about it, perhaps someone will help with part of the mechanics or hint you on how to reach your goal!