I'm not fully sure on how to help, however here is some suggestions:
you should give a background knowledge on your 1st paragraph and give your claim on gun violence. If your claim is against guns, state that in your 1st paragraph. For your 2nd paragraph give evidence to support your claim, give details on how guns are harmful, give examples on what way. For your 3rd paragraph explain how the evidence fits with the claim.
good luck! :)