Depending on what type of call-to-action you have used, a few things could happen.
If you've used a form Sniply, they will see a message that says "Thanks!" replace their text in the form. If you've used a button, link or image call-to-action, the user will be delivered to the page that you've set as the target page for the call-to-action.
One more thing will happen, only if you are on the free plan. After they return to the tab containing your Snip (after visiting your call-to-action's site), your reader will see a message explaining what Sniply is and giving them an opportunity to try Sniply. We do this only after you've gotten your conversion so that you don't lose anything by us showing the message. We are trying to help educate people about what Sniply is and how it might also be beneficial to them, so we've tried to make the message as convenient and unobtrusive as possible. Below is a screenshot of the message: